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THE PLANETS: 

SOLVED AND UNSOLVED PROBLEMS 

by D, Ya. Martynov 

"Nauka" Press, Moscow, 1970 



NATIONAL AERONAUTICS AND SPACE ADMINISTI^ATION - WASHINGTON, D. C. . MAY 1972 



TECH LfBRARY KAFB, NM 




NASA TT F-698 



THE PLANETS: SOLVED AND UNSOLVED PROBLEMS 



By D. Ya. Martynov 



Translation of "Planety: Reshennyye i 

Nereshennyye Problemy." 

"Nauka" Press, Moscow, 1970 



NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 



For sale by the National Technical Information Sen/ice, Springfield, Virginia 22151 

$3.00 



lllllllllll I I I I nil I I I Ml II nil I 



TABLE OF CONTENTS 



PAGE 



1. INTRODUCTION 1 

2. PLANETARY SURFACES 7 

3. PLANETARY ATMOSPHERES 25 

4. INTERNAL STRUCTURE OF THE PLANETS 41 

5. INVESTIGATION PROCEDURES AND POINTS OF APPLICATION 53 

TABLES OF PHYSICAL CHARACTERISTICS OF THE MAJOR PLANETS 

AND THE MOON 72 

MERCURY 72 

VENUS 74 

EARTH 76 

MARS 78 

JUPITER 80 

SATURN 82 

RINGS OF SATURN 84 

URANUS 85 

NEPTUNE 87 

PLUTO 89 

THE MOON 90 



iii 



THE PLANETS: SOLVED AND UNSOLVED PROBLEMS 



D. Ya. Martjmov 



ABSTRACT. A survey of the resolved and unresolved 
problems of planetary physics is presented. The con- 
tribution of worldwide research in the fields of 
astronomy, surface astronomy, space technology and other 
fields to planetary physics is reviewed. A list of 
physical constants for all planets and their satellites 
is given. 



* 



1- INTRODUCTION 

Since the planets of the solar system have become the topic of space /_3 
investigations, interest in them has grown to an extraordinary degree. Studies 
have begun to be made both from spacecraft flying near them and by scientific 
equipment in direct contact with the atmosphere or ionosphere of a planet and 
even with its surface. 

Planetary research has vmdergone a development which can only be de- 
scribed as explosive. Only this explosion is creative rather than destruc- 
tive. The size and pace of the investigations, which in the quite recent 
past have been purely academic, have given way to extensive experiments and 
to ardent, sometimes hasty discussions of the results extracted. The 
approaching possibility of interplanetary travel has had a mysterious, but 
very active effect on all these events. 



* 

Numbers in the margin indicate pagination in the original foreign text, 



Astronomers, design engineers, scientists representing related sciences, 
and simply inquisitive persons, are all showing interest. Correspondingly 
the number of scientific investigations has grown and extensive new informa- 
tion, based on the observations, has appeared. An avalanche of new facts 
has fallen upon us, some important, and some minor, some substantial and 
others secondary, some true and some doubtful. 

Just as for a ship at sea or an airplane in the air, the most hazardous 
part of the voyage for an interplanetary craft is the beginning and the end. 
But in transit the craft is also confronted with a difficult problem, to 
maintain a proper course and not deviate from it. Engineers designing space 
rockets and interplanetary scientific stations and ballistics engineers who 
determine the motion of the rockets at the beginning, enroute, and at the 
finish, have all turned for information to astronomy. All previous accom- 
plishments in astronomy have been mobilized to solve what is essentially an 
engineering problem — that is, to move a spacecraft toward a given target. 
Here precise knowledge is needed on the structure of the solar system and 
its dynamics, and a linear scale of interplanetary distances is needed in 
order to accurately utilize the precepts of celestial mechanics. These 
methods are used to determine the rocket's trajectory. The observational 
procedures of astronomy are also needed, as are the facts already extracted /4 
concerning the physical nature of planets and interplanetary space. 

All these achievements of classical astronomy were mobilized to serve 
the new problems created by mankind. Astronomy, this most ancient of 
sciences, is still the center of attention even today. Only now the re- 
quirements imposed on accuracy of the answers are immeasurably greater than 
before. The responsibility of astronomers has grown to include forecasting 
the conditions involved in the motion of spacecraft, their launching and 
landing. On the other hand, the landing of a space missile equipped with 
scientific equipment, or even its orbit near a planet, as the successful 
fligjits of the Soviet and American unmanned interplanetary stations showed, 
will return a huge amount of highly reliable new facts. The success of these 



flights has been tremendous. It has generated the Idea that the surface study 
of planets is henceforth a thing of the past, and must give way completely to 
space technology methods. 

A tragic delusion! Considerable time must yet pass before even the 
nearest planets can be studied exclusively with spacecraft, and the more 
distant ones will be studied for many years to come by surface methods that 
only will be developed and refined along with the space technology methods. 
It is these experiments, that is, those on the surface of the Earth, that will, 
to a significant degree, determine the topics of space experiments involved 
in studying the planets. 

The situation has not changed even following the latest success in 
astronautics, that is, the landing on the Moon by the crew of "Apollo-11" 
and its return to Earth carrying rock samples from the lunar surface, miles of 
photographic film and results of observations carried out on the surface of 
the Moon for a period of two hours, while the instruments which they left on 
the Moon have continued to carry out the experiments set up there. The crew 
of the "Apollo-11" brought to Earth new information which is distinguished 
by its high degree of reliability, but how little this is in comparison with 
the knowledge we must have about the entire Moon and all of its geographic 
(or more precisely, its "selenographic") and physical properties! This will 
all be possible only after trips to the Moon have become regular scheduled 
flights. 

Then does planetary research involve only the concept of interplanetary /5 
travel? The answer to this question can only be a negative one. The primary, 
and even ultimate, goal of any natural science is that of solving the origin 
and development of the topics and phenomena to be studied. And astronomy, 
as a subdivision of planetary research, has the fundamental problem of 
explaining how and when our planetary system came into being around the Sun, 
how it evolved, and how it will be in the future. To solve this problem, it 
is essential to have knowledge about the planets: In addition to the usual 
characteristics such as mass, size, form, and rotation period, it is necessary 



to know the structure and chemical composition of the surface of a planet, ^ 
its temperature, as well as the temperature of the atmosphere, and the 
qualitative and quantitative composition of the atmosphere. Attempts must 
be made to discover the internal structure of the planets and the relationship 
between planetary matter and comets, meteors and other interplanetary matter, 
based on the external characteristics. 

The study of the dynamics of planetary atmospheres greatly contributes 
to the field of climatology, since it reveals the possibility of imderstanding 
the motions characteristic of planetary atmospheres, as well as motions 
unknown on Earth. 

All this may be studied from the Earth's surface with great success, 
and, in fact, is. being studied by astronomers. But space technology pro- 
cedures are of Invaluable assistance. However, let us not cherish the vain 
hope of expecting in the near future, "at last". . ."from now on...", "now — ", 
etc. , that we shall know everything we wish to know about the planets, their 
formation, and their evolution. Being on Earth, we are developing a whole 
branch of science — geophysics — dedicated to the Earth itself, but we are 
infinitely far from being satisfied with the knowledge gainedl As yet we 
have no widely accepted concept as to the bowels of the Earth, its chemical 
composition and temperature at great depths. We can not even solve beyond 
doubt the question as to whether the origin of petroleum is cosmic or organic, 
and we still often err in the forecasting of weather. The list of such 
unresolved problems could continue without bound. 

In the present booklet we wish to give a survey of the resolved and 
imresolved problems in planetary physics that are of the greatest Interest 
today. We must say that these do not always coincide. For example, the 
degree to which the surface layer of a planet is friable is interesting, both 
theoretically and practically. Theoretically, because to some degree It 
determines the temperature conditions of the surface layers of the planet, 
and practically, because the conditions for landing a spacecraft depend on 
it. But in the first Instance the astronomer is interested in the nature of 







- ■*-'Jti 

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Figure 1. First men on the Moon. Expedition 
of the space ship "Apollo-11". Landing 
module; "Eagle" on the Moon, July 21, 1969. 
Astronaut Aldrin near seismometer he set 
up, equipped with solar batteries. Left 
center shows instrument for reflecting 
laser beam. Rear part shows imprint of 
Aldrin' s boots on the Itmar soil. 



the surface layer, its petro- 
graphic structure, thermal 
conductivity, etc., and in the 
second instance he is concerned 
with its capacity to withstand 
a dynamic and static load. The 
answer to the practical question 
of strength may be given with /7 
the answer to the first — a 
theoretically significant 
question — but, unfortunately, 
it is far from having that 
degree of reliability and 
accuracy which the designer 
must have. It is not surprising 
that the paths of astronomical 
and design problems often co- 
incide in the area of planetary 
research, although the means 
for solving them are not always 
identical. 



In this survey, we shall not give a systematic discussion of the facts 
and methods employed in planetary research — this is the concern of text- 
books. We shall speak about the latest successes and achievements in studying 
the planets, making reference to the surface methods, since space technology 
methods are quite widely known. And for this same reason the Moon will not 
be a matter of special concern, because formally the Moon is not a planet, 
but a satellite. The Moon is becoming an ever increasing topic of direct 
investigation. But any systematic investigation of the Moon by such means 
is a long way off I 



With this booklet, the author addresses himself neither to the reader 
v*io is a specialist in astronomy, nor to the reader who is making his first 



steps in planetary astronomy, but rather to the reader who has general 
knowledge as to the current state of the art In planetary science. The 
present essay may perhaps permit the reader to evaluate the degree of 
reliability of his knowledge and direct his attention to those fundamental 
problems which are still to be solved by the methods of surface astronomy. 



''• PLANETARY SURFACES 

Our knowledge of planetary surfaces is limited to the inner planets, or /8 
planets of the Earth group as we still call them — that is. Mercury, Venus, 
and Mars. We can also include the Moon among them. On Jupiter, for example, 
all that we can see are atmospheric and cloud formations. It would appear 
that we might say the same with respect to Venus, since we can see only its 
cloud layer, which is very thick and has almost no opening. But in quite 
recent times, by using radar impulses, it has been possible to penetrate 
the atmosphere of Venus and, reflected from the solid surface, to return to 
Earth the first information on the various formations on the planet's surface. 
It has now become possible to compile the first schematic map of Venus where 
individual features are shown, although it is true these features have as yet 
not been interpreted. But the map of Mercury, compiled from visual telescopic 
observations (Figure 2) , contains only dark formations on a light background, 
the nature of which is completely unknown. 

Ultimately, it is the observations from a planet's surface or stable 
atmospheric formations that will permit the period of rotation around its 
axis to be determined. This period, in conjtmction with the mass, dimensions, 
and shape of the planet, will offer the first signs of its internal structure. 
Along with this, the alignment of the axis of rotation is derived from such 
observations and it becomes possible to map the planet. 

At the present time, we already have at our disposal the correct values 
for the periods of rotation of all the major planets including Mercury and 
Venus, the data for which were obtained only by using radar (see page 54 
for details). The 59-day period, found for Mercury, indicates an angular 
velocity of rotation equal to the angular velocity of its motion around the 
Sun at perihelion, that is, on that orbital segment which is nearest the Sun. 
Tidal forces have apparently played a role in establishing such an equation. 




T 









^° a?* &r f20' m" 130° 210" 2W 170' Ja7°. 3S0° 






Figure 2. Map of the surface of Mercury, com- 
piled by 0. Dolfuss from observations at the 
observatory Pic du Midi (France) . 



The 243-day period of 
Venus' retrograde rotation is 
coupled with the rotation 
period of Venus and Earth 
around the Sun, such that 
at each minor conjimction of 
Venus — that is, when Venus 
is located between Earth and 
Sun — the same side of Venus £9^ 
is turned toward Earth. The 
Earth occupies the same 
position above the horizon 
from some point on the surface of Venus every 146 days, and the minor con- 
junctions of Venus are repeated every 584 = 4 x 146 days. As to whether this 
alignment is random or not, we still do not know. 

It is interesting that the previous visual observations of Mercury 
resulted in a period of rotation around its axis of 88 days, equal to the 
period of its rotation around the Sun. It was found that Mercury has the 
same side always turned toward the Sun. This conclusion is no longer valid, 
but all the ancient drawings of Mercury's surface which previously served for 
its mapping with an 88-day period, surprisingly enough, are satisfactorily 
encompassed by the new period of 59 days. It seems that such a situation is 
due to in determinancy in the drawings, which in turn, is due to the problems 
involved in observing Mercury. 

We have today maps of the surface of Mercury and of Mars. That of 
Mercury is very crude, but the map of Mars contains numerous details, the 
comparison of which at different oppositions indicates a substantial time- 
variability in the face of Mars, not only due to variations in time of year 
(Martian), but independently of them, as well. 

Of course, the most detailed maps are these of the Moon; global maps /lO 
have been com.piled in scales of 1:5,000,000 and 1:10,000,000. For individual 



8 




Figure 3. Map of the surface of Mars In 
oppositions of 1956 and 1958. South - 
above. In 1956 Mars had mainly its south- 
ern hemisphere turned to the Earth. On 
the 1958 map, the aerographic latitudes 
are shown on the left and the longitudes 
at the bottom. 



regions, larger scale maps 
have been compiled which were 
produced by the flights of 
spacecraft around the Moon. 
A map of the equatorial zone 
has been compiled for the 
visible side of the Moon in a 
scale of 1:1,000,000. Here 
terrestrial and space inves- 
tigations successfully work 
together: to compile large- 
scale maps with the aid of 
highly informative photographs 
taken at close distances, a 
large number of reference 
points is required, the 
position of which is determined 
on the surface of the Moon 



(selenographic coordinates) from ground observations, connecting the reference 
points with the circumference of the lunar disk and thus with its center. 



To map the dark side of the Moon only space methods can be used, and 
cartographic continuity requires photography which will Include part of the 
visible side of the lunar surface and part of its dark side in a single frame, /ll 
Naturally, it is those points on the visible side which are found near the 
edge of the lunar disk in observations from Earth that are photographed in 
such an instance. Determination of the selenographic longitude for these 
points may involve considerable errors, which then cause the longitudes of 
features on the dark side to be in error. Because of this, it was found 
that the longitudes determined from data of the Soviet and American space- 
craft (Luna-3, Zond-3 and Lunar Orbiter) differed by up to 7°. In linear 
dimensions, this represents 200 kilometers. Of course, such discrepancies 
are not allowable, and they were eliminated in further investigations. 




l«i<C\f !3---.-i--;L*-. -=-,•,.••.■ '■■--■ -.'-^^ t.;' •>'..,-. - ■ , '.- 



1 






















Figure 4. Part of the surface of Mars at a 
distance of 3500 km. Photograph taken by 
the unmanned spacecraft Mariner-6. 



The achievements of the 
unmanned interplanetary sta- 
tions of the "Mariner" series 
(Nos. 4, 6, and 7), which 
revealed numerous circular 
mountains very similar to such 
formations on the Moon, have /12 
forcibly advanced problems which 
we call geomorphological prob- 
lems with respect to Earth. 
The morphology of a planetary 
surface reflects its past 
history. The similarity in 
the surfaces of Mars and the 
Moon, of course, indicates a 
similarity of formation. 
Their differences, caused 
mainly by the existence of an atmosphere on Mars and the lack of one on the 
Moon, are of considerable interest. The total number of circular formations 
per square kilometer of the surface of Mars is the same as on the lunar 
continents, although small formations with diameters from 20 to 3 km are more 
numerous on the Moon. Since the formations that are less than 3 km in size 
are not distinguishable on the Mariner-4 photographs and not all objects with 
dimensions greater than 3 km (approximately up to 10 km) can be recognized 
on these photographs, we can only guess as to whether their small number 
is a result of observational selection, or is a result of their obliteration 
under the influence of winds, distortion from meteoritic impacts, or by 
thermal stresses. With Mars being near a ring of asteroids, we might expect 
a considerably greater number of circular mountains on it, but if this is 
not true and the efficiency of the above landscape obliteration is unknown, 
then the hypothesis of an endogenous or volcanic origin of the craters 
becomes plausible • No matter what the true situation is, all the detailed 
photographs of the Moon at close distance only strengthened the opinions of 
those who considered that the lunar landscape was formed under the action 



10 



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Figure 5. Mars at a distance of 90 
million km (Pic du Midi, France, 
1967) and 920,000 km, July 29, 1969 
(Mariner- 6, below) . 



of both internal effects (vulcanism, 
tectonics) and external effects 
(incidence of meteoric bodies) . 

The different radioactivity of 
the various lunar formations obtained 
in the lunar orbits of our unmanned 
space stations Luna-10 and Luna-12 
speaks in favor of the first hypo- 
thesis. This difference indicates 
that basic rocks predominate in the 
seas (basalts) and ultrabasic rocks 
on the continents. The first probably 
has a high amount of iron (the so- 
called ferrobasalts) . As a whole, 
as chemical analysis of the lunar 
soil made by the Surveyor, the Luna-9, 
and the Luna-13 showed, the lunar 
surface rocks are the result of fusion. 
Analysis of the composition of the 
samples collected at the landing site 
of the Apollo-11 in the Sea of 
Tranquility revealed a rather high 
petrographic diversity and, in general, 
a significant similarity to igneous /13 
rocks on Earth, if we do not consider /14 
the very high titanium (TiO„ up 10% 
by weight), Zr, Y, and Cr content 
with a significant sparsity of alkali 



metals Na, K, and Rb. These volcanic specimens contain numerous gas cavities, 
about 50% clinopyroxene, about 30% plagioclase, a large amount (up to 15%) of 
ilmenite and granular impregnations of olivine, and sometimes iron-nickel 
spheres. These can be included in the olivine-containing basalts. But there 



11 



are basalt specimens which contain no olivine. Under terrestrial conditions, 
basalt lavas are smoothly extruded. 

Along with the basalts, the Investigated lunar specimens contain 
breccia type rocks which consist of cohesive angular fragments less than 0.5 
cm In size. Traces of microfractures and numerous vitreous Inclusions can 
be seen here. Their structure Is commensurate with the thesis that they 
were formed by the powerful Impact of a body on the lunar surface, falling 
onto the Moon from outer space. 

In general, the rocks collected on the Moon reveal traces of erosion 
(Impact?) on the upper surface, whereas the lower surface has apparently 
remained unchanged. Analysis of the age of specimens from the Sea of Tran- 
quility (for the potassium: argon ratio) indicates that they were crystallized: 
from three to four billion years ago; that is, they are older than the most 
ancient of terrestrial rocks. According to the traces which cosmic rays have 
left in them, these specimens had been at a depth of more than a meter under 
the surface during their entire existence except for the last 20-160 million 
years; that is, they were ejected to the surface either as a result of 
meteorltic erosion or as a result of tectonic processes. 

The fact that the upper cover of the Moon still lives and "breathes" 
today is Indicated also by the optical phenomena repeatedly mentioned by 
observers during the time of telescopic observations of the Moon (such 
phenomena are numbered at about 600 Jover three-and-one-half centuries) and 
especially the generation of gases in the region of the crater Alphonsus 
mentioned by N. A. Kozyrev in 1958 during spectral observations. In order 
to reliably answer the question of the authenticity of rapid changes on the 
surface of a planet or of the Moon, we must have simultaneous observations at 
several astronomical stations separated from one another in longitude by 
90-120° and directly connected with one another by modern communication /15 
facilities. 



12 



We should mention that the 
combined influence of the internal 
and external factors in the 
formation of the lunar landscape 
(just as for Mars) is apparently 
inescapable, since the impact of 
a large meteorite will arouse 
volcanic activity in that region. 



The number of craters on the 

Moon is so high that they can 

never be considered to be only 

Figure 6. Surface of the Moon, taken at a the result of the impact of 
close distance with a television camera 
on the unmanned spacecraft Luna-9. 




asteroids and large meteorites, 
which occurs rather rarely. It 
would be more proper to credit the formation of the craters to that era when 
the Moon was just forming and many plane tesimals, as yet unabsorbed by the 
planets, were moving around it. When the Moon absorbed them, circular 
mountains of various dimensions were formed. Gradually a state of saturation 
was established, when any new impact would annihilate the older craters and 
create new ones. In fact from one (in time) impact several ejections may 
occur which either form a chain of several craters, or only one which is 
elongated in the direction of the ejections — as, for example, the crater 
Schiller in the southwest part of the visible lunar disk. The large number of 
small craters arranged around the crater Copernicus are undoubtedly of 
secondary origin. They were formed as a result of the explosive dispersion 
of lunar matter when the basic crater was formed. 



J16 



These craters can be easily discerned on the dark background of the 
Oceanus Procellarum. This same dark coloration of a different degree of 
saturation is possessed by all the seas on the Moon, their surface is 
comparatively smooth, and they are either devoid of craters, or have very 
few. The reason for this sparslty is the age of the seas. These are young 
formations, formed about two billion years ago, on which numerous large 



13 



bodies, preserved until the later stages of development of the solar system, 
left traces of the impact. However, in the very youngest formations, such 
as, for example, the craters Tycho or Aristarchus, the surface is very 
uneven and covered with large fragments. With time, they will be broken up 
and acquire a fine structure on an overall smooth background, and only 
massive impacts will disturb this picture. New impacts will disturb the 
already existing formations by different means, that is, by direct impact 
or by secondary Impacts during dispersion. The lunar surface has undergone 
events of such nature many times during its existence, and very ancient 
objects have gradually disappeared. Only the largest of them, many hundreds 
of kilometers in thickness, can still be traced in our time. 

Although on the Moon, in contrast to the Earth, the changes on the 
surface take place with extreme slowness because of the absence of weathering 
and erosion, the Moon, nevertheless, is not a museum. It is externally 
vulnerable, and the effect of external factors continuously changes its face. 
Therefore, we can understand that those lunar formations, whose age exceeds 
four and one half billion years, have not been preserved up to the 
present. 

Craters are also encountered on the Moon which are similar to volcanoes 
on the Earth (around this same Copernicus) , and sometimes they are quite 
numerous. It is assumed that at times lava flows from them, but these 
processes are of a local nature and determine the lunar landscape to only a 
small degree. 

The soft landing on the Moon of the unmanned space stations, Luna-9, /17 
Luna-13, and the Surveyors, not only gave information on the chemical com- 
position of the lunar cover, but also established its macroscopic structure, 
that is, finely crushed bunches, dust particles (about 10 y) , in which small 
and large fragments and basic lunar rocks are imbedded. Contrary to former 
concepts, they are weakly bonded and by no means form strong strata, con- 
sisting of minute grains. Very fine dust, in fact, does cover everything on 
the Moon — the finely crumbled surface and rocks, but the supports of the 

14 



"Eagle" (see Figure 1) sank only 5-7 cm Into the ground and the astronauts' 

feet sank only several millimeters. In an attempt to sample depth, a steel 

tube was sunk 5-7 cm without difficulty, and only with a great exertion of 

force was a depth of 20 cm reached, but the core samples taken were found to 

be finely structured. The crew of Apollo-12, which landed in Oceanus 

Procellarum, encountered a more friable surface layer. The density of the 

friable surface material of the Moon, as the samples showed, was altogether 

3 
0.8 g/cm , and beneath them, starting at a depth of 5-10 cm, the density 

3 
reached 1.5 g/cm . Finally, the density of the rocks and stones lying on 

3 
the surface was equal to approximately 2.8 g/cm . As radio observations of 

the Moon show, the density of its surface layer gradually increases with 

depth and reaches the density of the underlying rocks at a depth of one to 

several meters. The surface layer is thicker in the seas — up to ten 

meters. With all the similarity between the Martian and lunar landscapes, 

we can hardly expect the same surface structure on Mars. The existence of an 

atmosphere makes it impossible for the dust particles to adhere, as this is 

inevitable in a vacuum. The surface of Mars must have a more friable 

structure, and this is confirmed by radar observations which indicate an 

incomparably greater smoothness on it than on the Moon (see page 17). 

If it has become possible to obtain information, using unmanned space 
stations, on the chemical composition and also to study the structure of the 
upper cover of the Moon, then its petrographic compositions are derived 
mainly on the basis of analogies from photometric, spectrophotometric, and 
polarization observations. These analogies in the majority of cases are /18 
loose, since the result is usually ambiguous, and, furthermore, the color /19 
varies depending on the degree to which the matter is broken up and depending 
on the ultraviolet radiation or proton radiation. So, for example, the 
almost universally accepted conviction that the surface of Mars is composed 
of limonite (pe -nH^O), based on the similarity of many spectrophotometric 
and polarization characteristics, is encountering difficulty today, since 
with advanced investigations new characteristics are being discovered that 
do not coincide for Mars and for limonites. 



15 



No less ambiguous are the 
results of radio obseirvations 
of the natural thermal emission 
from the planet in various 
ranges . Emission at long waves 
comes from the subsurface strata. 
The phase lag in the maximal or 
minimal temperature and the 
variation in the mean diurnal 
(on the Moon — monthly) tempera- 
ture with wavelength (or what 
amounts to the same thing, with 
depth) gives the possibility of 
judging the thermal conditions 
of matter on the planet's 
surface layer at various depths, 
and its thermal and electrical 
properties. Unfortunately, only 
the rather complicated quantity, 

the coefficient of thermal 

-1/2 
conductivity y = (XP^) > is 

amenable to direct determination; 
this coefficient connects the 
coefficient of thermal conduc- 
tivity x> density p and specific 
heat c of the material. As yet 
this method has given specific 
information only about the Moon. Averaging which is too broad is obtained for 
the planets over practically the entire hemisphere of the planet; it is 
difficult to eliminate the influence of the atmosphere. In its application 
to the Moon, this method gave a result that is in accordance with other 
methods; its surface is composed of finely crushed rocks. The temperature 
gradient is sizeable, thus indicating a heat flux from the depths of the 
Moon. Using reasonable values for two of the three quantities X» P> c, we 




Figure 7. Large (0.5 m) rock on the surface 
of the Moon (Photograph taken by the un- 
manned spacecraft Surveyor-1) . 



16 



can find the third and then seek rocks which have the appropriate properties. 
However, in this case there is still a wealth of choices to be made. 

Narrowing the range of solutions is only possible after a systematic 
direct investigation of the various sites on the lunar surface becomes 
possible with the aid of spacecraft that have landed there, including manned 
craft. Comparison of the radio observations and the results of direct 
analyses will make it possible to standardize the radio observations, that 
is, to establish a correlation between real rocks and their radio emission. /20 
Later this standardization can be applied to an analysis of the radio ob- 
servations from Mars and Mercury. The use of radar methods has been of 
substantial aid for this purpose; these methods make it possible to study the 
reflectivity of the component rocks. 

The radar technique is effective also in solving the question of the 
degree of roughness of the planetary surface. Two mechanisms operate in the 
reflection of radio waves, that is, quasimirror reflection from large-scale 
irregularities (without disruption of coherence) and disordered scattering 
on small-scale heterogeneities, whose dimensions are on the order of magnitude 
of the wavelength. The first is performed along the normal, since the 
transmitting and receiving stations either coincide or may be spaced over 
the Earth, which even from the Moon is visible at an angle less than 2° . If 
the slopes on the planet are generally not high, coherent reflection will 
take place only from a small region in the center of the disk, such that the 
site of the reflection may be established with complete confidence. Scattering 
on small surfaces is disordered, strongly damped and unpolarized, which 
permits distinguishing it without difficulty. On a comparatively rough 
scale (A ~ 70 cm) the smooth slopes are 3° for Mars, 6° for Venus, and 10° 
for the Moon and Mercury. As applied to Mars, the photometrically processed 
photographs obtained by Mariner-4 led to the conclusion, from fluctuations 



We mean here the inclinations of the lateral slopes of the surface 
formations toward the horizontal plane. 

17 





















Figure 8. Radar picture of the 

vicinity of the lunar crater Tycho, 
taken at the radioastronomy ob- 
servatory at Haystack. The picture 
permits distinguishing details 
having a dimension of 1 km. Unlike 
an optical picture, the details 
here are differentiated from one 
another based on their ability to 
reflect the radio signal sent from 
the Earth (wavelength of 3.8 cm). 
Not only is the reflectivity in 
Itself manifested, but also the 
slopes of the reflecting elements 
to the line of sight, since large 
details have a specular reflection 
and if the corresponding surface 
is not perpendicular to the inci- 
dent beam, it is either not 
reflected back in the same direc- 
tion, or a weak diffusely reflected 
signal will be obtained. 



in brightness as a function of the 
angle of elevation of the Sun, that 
on a scale of 3 km and higher the 
slopes in the irregularities lie in 
the range of 1-3°, although on the 
slopes of the craters. Inclinations 
of up to 12° are possible. 

Polarization of radio waves, 
reflected from the edge of the planet's 
disk, as well as from its natural 
radio emission, makes it possible to 
determine the dielectric constant of 
the planetary matter and thus narrow 
the scanning range for the material 
comprising the surface. 

As applied to the Moon, the 
complllation of the radar chart was 
found to be fully successful. At a 
wavelength of X = 3.8 cm, a resolving 
power on the order of 1 km was 
attained, which approaches the re- 
solving power of optical astronomy. 
Figure 8 shows such a map, compiled 
at the Haystack station (USA) and 
showing the distribution of the 
reflectivity (by no means light and /21 
dark) in the region of the crater 



Tycho. In order to obtain similar 
results with respect to the planets, much more powerful telescopes are re- 
quired (at least two orders of magnitude larger) , since the planets are two 
orders of magnitude farther away than the Moon; correspondingly the direc- 
tionality of the radio antenna must be raised by two orders. In this case 



18 



the same strength of the reflected signal will not he attained; this signal 

grows only in proportion to the root of the fourth power of the antenna /22 

cross section. Even today, the sensitivity of the apparatus used in radar 

is admirable; the radio impulse reflected by Venus is so weak that it is 

impossible to find it directly. It is discernable only by complicated 

computational analysis. Its energy is similar to the work of one step of a 

mosquito. 

Mars, whose surface has been most studied after the Moon, leaves a 
number of unresolved problems, among which the important ones are the 
questions concerning the nature of the polar caps and the cause of seasonal 
variations in them. In this connection, we have not mentioned the nature of 
the canals on Mars, since after almost one hundred years of discussion, the 
"public opinion" of the astronomers tends to believe that the canals are the 
result of schematizatlon in drawings (or examining photographs) of Mars. 
It is an involuntary geometrization introduced by the observer into the 
picture of the distribution of extremely weak and unclear details. 

After obtaining photographs of Mars at close distances with the aid of 
the unmanned spacecraft Mariner-4, Mariner-6 and Mariner-7, which revealed 
no signs of such canals, the question as to the canals on Mars can be 
considered "closed". 

As we know, the atmosphere of Mars contains water vapor in a small 
amount, and mainly carbon dioxide (see below). This gives a basis for assuming 
that the polar caps of Mars consist of snow or of solid carbon dioxide. 
The temperature of the Martian surface at the poles allows either assump- 
tion. The spectral observations favor snow. In the light reflected from it 
there are absorption bands with a wavelength of about 1.4 and 1.9 y. The 
same is observed in the spectrum of the polar caps of Mars. The character of 
the light polarization reflected from the polar caps of Mars is the same as 
in hoarfrost which is formed at low temperatures by means of direct conver- 
sion of the water vapors into the solid state. The reverse process, taking 
place with heating of hoarfrost, also leads to sublimation from the 

19 



solid state, without thawing into the gaseous state, and the remaining 
hoarfrost assumes a porous structure. Its very weak polarization is similar 
to that observed at the polar caps of Mars. 

In addition to this, we must remember that in the Martian atmosphere 
carbon dioxide is predominant and the very low temperature at the Martian 
poles (about 150° K) does not permit the carbon dioxide to remain in a gaseous /23 
state. Precipitation of the overwhelming part of it in the form of "snow" 
and dry ice Is unavoidable. Therefore, the main component of the polar caps 
of Mars is carbon dioxide mixed with water in the solid phase. A very small 
admixture of snow is necessary in order that significant bands are found in the 
reflected light with wavelengths of about 1.4 and 1.9 y. 

As far as seasonal variations in the dark "seas" of Mars are concerned, 
which have basically the same color as the light "continents", only with a 
lesser albedo, as we well know they are often attributed to the growth of 
plants with onset of the warm season, melting of snow, and moistening of the 
soil. Included in the sources of moisture, we have mentioned mineral water 
since all of Mars in terms of its mean temperature (see below) is located in 
a state of permafrost, thawing only at the top and for a short time in the 
middle and lower latitudes. It is difficult to call these processes anything 
other than biological processes which might vary the structure of the upper 
cover of the planet's surface as a function of time of year. In the absence 
of, or extreme sparslty of, free oxygen on Mars, vegetation there may exist 
only in the simplest forms. Spectral investigations, unfortunately, have not 
helped solve this question, but the polarization investigations which 
indicate, first of all, the structure of the reflecting surface foster the 
assumption of mass breeding of small organisms in the form of opaque granules 
Including sporous plants — algae, Cetrarla caccullata, and fungi. The 
precipitation of crystal formations would give a completely different 
polarization picture. 

The extraordinarily low contrast of the individual segments on the 
photographs of Mars, obtained by Mariner-4, fully correspond to the picture 

20 



long-mentioned by Earth observers, that Is, the extreme "grayness" and the 
insignificance of the details on Mars during the winter season. Marlner-4, 
orbiting Mars, photographed primarily its southern hemisphere, when winter 
prevailed there. Mariner-6 and Marlner-7 were in the most favorable position 
— their photographs were much better: Marlner-6 photographed mainly the 
northern hemisphere where at this time It was early fall, and Marlner-7 
photographed the southern hemisphere where it was early spring. 

Radar observations of long-range reflection of the emitted signal ,„, 
reliably revealed the irregularity of the relief, reaching 12 km on Mars. 
We should not be surprised at this. The differential in heights on the small 
Moon is not any less. If the depressions on Earth were not filled with the 
ocean, the height differential externally observable between the Himalayas 
and the Phillipine trough would reach almost 20 km. But on Venus, radar did 
not reveal any altitude difference greater than 2 km. It is true this refers 
to the topography along a certain parallel, for which the Earth was at 
zenith during the observations. On other parallels, the situation may be 
completely different I 

In finishing this examination of the questions involving the structure 
of planetary surfaces, we should emphasize that the tempting possibility of 
making an analogy here with the structure and composition of meteorites is 
dangerous, since it is quite doubtful that meteorites are fragments of large 
planets. They have never been subjected either to the effect of very high 
pressures or to that of high temperatures. 

Determination of the absolute values of the temperature of the planet's 
surface Is very specific. Optical methods based on measurements in the 
Infrared band of the thermal flux, coming to us from the planet, give a 
comparatively high degree of resolution by cross section. In particular, on 
the Moon numerous "hot" points have been detected which are revealed by slow 
cooling at sunset or in the process of lunar eclipse — this is direct proof 
of the absence of a thick heat-protective dust cover at these sites. 



21 



But only as applied to the Moon and Mercury which have no atmosphere 
does this path lead directly to the target. As applied to Venus, the 
measurements of thermal flux in infrared rays gave a temperature of about 
240° K, referring to the upper troposphere rather than to the surface, and as 
applied to Mars — a surface temperature, slightly distorted by atmospheric 
influences. Measurements of thermal flux in the radio band are free of this 
disadvantage to a much larger degree, but they are also not without fault. 
This is because, in the centimeter and millimeter bands, the radio waves are 
absorbed in the atmospheres of the planets, and in the decimeter and decameter 
band the ionosphere, if it is sufficiently dense, may introduce disturbances. 

It is just such a situation that was created in interpreting the /25 
measurements of the radio emission originating from Venus. At wavelengths 
from 3 to 10 cm, the measurements give a brightness temperature up to 700° K 
and above, but at the shorter wavelengths it is much lower, below 300° K. At 
the 21 cm wavelength, a drop in temperature is also observed. A ten-year 
discussion accompanied by ever newer and newer measurements have led the 
majority of astronomers to the conclusion that only the measurements in the 
3-10 cm band pertain to the solid surface of the planet. The shorter waves 
are absorbed strongly in the atmosphere; therefore, the temperature of 300° K 
pertains to the upper atmospheric layers. However, only the direct tem- 
perature measurements in the atmosphere of Venus carried out in the brilliant 
experiment of the Soviet unmanned spacecraft Venera-4 — and the proofs thus 
found that Venus has no significant ionosphere (it exists only on the day- 
light side and is apparently caused by solar x-ray radiation) — finally 
convinced everyone that the surface of Venus is in fact very hot, and placed 
before theorists the problem of explaining this fact. 

Measurements on the large radiotelescope at Pulkovo, the flight of the 
American unmanned craft Mariner-2 near Venus and, finally, the interfero- 
metric measurements with a high resolving power at the 10 cm wavelength have 
all made it possible to study the temperature distribution across the disk 
of Venus, although it is true it is only approximate and the results obtained 
by various means are not without contradictions. 

22 



The temperature on Mars was found to equal approximately 200° K which 
is the mean temperature across the disk, in a wide range of radio waves 
(3 mm - 20 cm). It would be interesting to trace, by radio measurements 
with high resolution, the existence of relationships between polarization of 
the emission and the progressive seasonal darkening of the Martian seas, 
visible during polarization observations in the visible band. 

Measurements of the natural radiation from Mars in the infrared band 
gave results similar to the results in the radio band, but not coinciding 
with them: for those places on the equatorial belt of the planet's surface 
where the Sun is at the zenith (subpolar region) a mid-day temperature was 
found in the range from 250 to 280° K at aphelion, and about 300° K at 
perihelion. Such differences should not be surprising, since the orbit of 
Mars is rather eccentric and at its perihelion Mars is located significantly /26 
nearer the Sun than at aphelion. The latest, more reliable measurements give 
lower values, which correspond better to the radio measurements — for 
example, for the entire illuminated hemisphere of Mars a mean temperature of 
225° K (at aphelion) was found. Furthermore, the temperature of the Martian 
surface undergoes very strong variations in the course of short days (ZA-tt 
hours) . During the day there, shortly after noon, it reaches a maximum of 
about +20° C; in the morning after the nocturnal radiation of heat into outer 
space, the temperature drops to -60° C. The reason for such a rapid cooling 
undoubtedly is due to the low density of the atmosphere (see below) that is 
incapable of retaining the natural radiation of the planet. The latest 
measurements by Mariner-6 revealed a new temperature of 150° K at the polar 
caps on Mars . 

New measurements of Mercury in the infrared band give a temperature of 
620° K for the daylight side. The dark side is no hotter than 150° K, but 
also is somewhat colder, which does not agree with the idea that there is no 
atmosphere on the planet and with the new correct value for the period of 
rotation, for which the solar days last 176 Earth days. In the event there 
is no atmosphere, the temperature during the night would have to sink much 
lower and then, in measuring the integral temperature across the disk of 

23 



Mercury, a notable phase effect would be observed — that is, a dependence of 
the measured temperature on the value of the unllluminated (night) part of 
the planet's disk. But the phase effect on the temperature of Mercury is 
very weak. 



24 



■ ■■IIIIH 11 I II UriMIII 



3. PLANETARY ATMOSPHERES, 

The existence or the lack of an atmosphere is strongly manifested in the /27 
many physical properties of the surface layers of a planet, that is, in its 
thermal conditions, formation of the planet's landscape, possibility for the 
evolution of life, etc. Furthermore, the chemical composition of a planet's 
atmosphere gives signs as to the past history of the planet. 

A planet's atmosphere is revealed by a fading of brightness toward the 
edge of the disk, by blurring, by clouds, etc., when simple telescopic 
examination of the planet is involved, but for quantitative determinations 
we must have measurements — photometric, polarization, and spectral. The 
photometric measurements are the simplest, but their interpretation will 
not provide a completely unequivocal answer, because the presence of suspended 
particles and aerosols in the atmosphere will somewhat complicate the theo- 
retically clear photometric effects of a purely gaseous atmosphere. In 
particular, it will lead to an exaggeration of the thickness of the atmospheric 
layer. The same can be said of polarization measurements. Neither measurement 
procedure will give any indication of the chemical composition of the atmos- 
phere . 

Incomparably more accurate and complete information is given by spectral 
analysis, both in ground observations, and especially when receiving equipment 
is launched into the stratosphere or completely beyond the confines of the 
Earth's atmosphere. Still more information is given by chemical analysis of 
the atmosphere carried out by equipment penetrating it, such as was done by 
the unmanned craft Venera-4, Venera-5, and Venera-6. 

A summary of our current knowledge on the chemical composition of 
planetary atmospheres is given on Table 1 on page 26. 



25 



TABLE 1. GASES WHOSE PRESENCE HAS BEEN DETECTED IN 
THE ATMOSPHERES OF PLANETS AND SATELLITES 



Gases 



Planet 


Gases 
CO2?? 


Planets 
Uranus 


Mercury 


Venus 


co^::, CO, n^, h^o. 


Neptune 




0^, HCI, HF 

N^::, o^:, h^o, Ar, 


Pluto 


Earth 


Satellites of 
Jupiter 




CO2 Ne, He, CH^, Kr, 
N2O, H^, 0, 0^, Xe 
CO^, CO, H^O, CO2 
ion, H, C, atoms 




Mars 


Titan (satel- 
lite of Saturn) 




Triton (satel- 
lite of Neptune) 


Jupiter 


H^, CH^, NH^ 




Saturn 


H^, CH^, NH^C?) 





^2' ^"4 
H^, CH^ 

No data 
No data 



CH, 
4 

No data 



There is every basis for assuming that a large amount of helium exists 
in the atmosphere of Jupiter. But its resonance lines are found in the far 
ultraviolet band, and the necessary excitation sources are lacking for the 
appearance of nonresonance lines, taking place from the excited levels. 
In precisely the same way, the existence of molecular nitrogen on Venus 
would be impossible to establish by means of ground observations, since its 
clearest spectral characteristics are found in the ultraviolet spectral band, 
which are completely blocked by the Earth's atmosphere. The existence of N„ 
on Venus was first established by Venera-4, just as 0„ and H„0, which had 
previously been detected only hypothetically. 



/28 



The unmanned space stations Venera-4, Venera-5, and Venera-6 reported 
reliable quantitative data: the equipment installed on them showed that the 
atmosphere of Venus is very hot, and in its composition carbon dioxide 
occupies about 97 +4%. The gases N„, 0„, and HO must be assumed as merely 



26 



Impurities. The numerical data should be assumed as approximate, since it 
is still not clear as to which level above the surface of the planet they 
refer. 

If we assume that Venera-4 discontinued transmission of information at an 
altitude of about 20-25 km, it is precisely to this level of Venus' atmosphere 
rather, than to its base, that we must attribute the measured values of T = 540° 
K and P = 18.4 atm. Then by extrapolation, we can find, for the surface of 
Venus, an atmospheric pressure near 100 atm and a temperature above 700° K 
with no unusual fluctuations from day to night. Almost the same data were 
reported by Venera-6: in the altitude range from 48 to 10-12 km the pressure 
varied from 0.5 to 27 atm, and the temperature from 300 to 600° K. If these 
data are extrapolated according to adiabatic law, then for the surface of 
Venus we will obtain a pressure of 100 atm and a temperature of about 770° K. 
Similar data are obtained on the basis of ground radioastronomical observa- /29 
tions. The data from Venera-5 differed rather strongly from these results. 
The reason for these deviations is still not clear. If we take the mean 
value from those obtained by Venera-5 and Venera-6 for the amount of water 
vapors equal to 0.05% over the atmosphere as an average, then their relative 
content in the atmosphere of Venus is found to be the same as on Earth, but 
the absolute value is found to be two orders of magnitude higher. However, 
in the Earth's oceans the amount of water contained is five orders of magni- 
tude greater than in the atmosphere. Therefore, we can confirm that the 
amount of water on Venus is significantly less (by three orders of magnitude) 
than on Earth. The same can be said also about oxygen. As far as the 
absolute content of carbon dioxide in the Venusian atmosphere is concerned, 
then it would approach in order of magnitude that which would exist in the 
atmosphere of Earth if all its carbonate rocks were to release the C0„ bound 
in them. To make a full comparison of the atmospheres of Earth and Venus, 
we must know the amount of virgin C0„ and H„0, which is constantly leaving 
the depths of the Earth into the atmosphere by volcanic eruptions. On the /30 
whole, if the entire atmosphere of the Earth is assumed to be the result of 
the generation of gases from the solid crust ("degassing") and we consider 



27 



V B IZ 



2i m s 



nnmTTrnrn-'niTiin Trr:rTi 
ff ;■ \ .^ \ ff J _„_... 

J L iiiL. :rii 



.ji^i? 



8710 



_m-o 



Figure 9. Spectrograms of Venus (upper) , Mars 
(middle) , and the Sun (bottom) (taken through 
the Earth's atmosphere) in the 8690-8730 A 
band, occupied by a CO- carbon dioxide mole- 
cule band, the lines of which (they are 
scaled at the top) are very sharply visible 
in the spectrum of Venus, much weaker in the 
spectrum of Mars and totally invisible in the 
spectrum of the Sun. The other strong lines 
of the spectrum are formed either in the 
atmosphere of the Sun or in the atmosphere of 
the Earth. 



that no chemical interaction 
with the crust and the bio- 
sphere has taken place, then 
we find a composition that 
is similar to that on Venus 
(and Mars) with the excep- 
tion of the excess of water 
on Earth which requires a 
separate explanation. 

Thus, the atmosphere 
of Venus also has a secondary 
origin, but probably with no 
biosphere. For the beginning 
of life on Earth, a reducing 
atmosphere was required (for 
example, with an abundance 
of methane CH,, hydrogen H., 
etc.). It would be inter- 



esting to seek prebiologlcal 
organic molecules in the reducing atmospheres of the major planets. It may be 

o 

that the absorptions at XA 2600 and 2100 A, detected in the spectrum of 
Jupiter, have precisely such an origin. 

Bearing in mind the difficulties in observing Venus from Earth, following 
from the fact that it is a minor planet which is near the Earth only when its 
dark side is mainly turned toward us, we must not exaggerate its cloud layer. 
In fact, photographs of the Earth, obtained in the past two to three years 
from the distance of the Moon to the Earth under favorable illumination 
conditions, and also from satellites at closer distances, can be interpreted 
by us only with difficulty and we are familiar with the map of the Earth, 
since it seems to be so covered with a cloud cover. Although the albedo of 
Venus is much greater than that of Earth, nevertheless, the veil of the 
Venusian clouds is not dense, which is proved by the diversity in temperatures 



28 



found by spectroscopic measurement of the C0_ bands on Venus: the tempera- 
tures are obtained in a wide range from 215 to 445° K, obviously depending on 
how free of clouds is the site of the planetary disk that is spectrographi- 
cally measured, and in the same manner at what great atmospheric depth the 
observable spectral bands originate. 

With the very slow rotation of Venus, its thick atmosphere must obey 
forms of circulation that are completely dissimilar to those in the Earth's 
atmosphere. Theoretical study of this phenomenon and its proof by observa- 
tions are of the greatest interest. However, the observations of Venus have 
established one type of atmospheric motion, similar to those on Earth, and 
judging from the motion of the dark formations in the cloud layer of Venus, /31 
the rotation period of the atmosphere at this level comprises four Earth 
days in the same (inverse) direction as the rotation of the planet itself. 
This indicates winds of great force in the upper troposphere of Venus, moving 
at a velocity up to 100 m/sec In the direction of the planet's rotation. 

Now we understand in rough outlines the atmosphere of Venus, but the 
details remain very unclear. Including the nature of the cloud cover on /32 
Venus and its role in the transport of radiation from the Sun to the surface 
of the planet and back into space. Now that we have proved the existence of 
water on Venus, due to the experiments with the unmanned spacecraft of the 
Venera series, more than ever we can assume that the clouds on Venus are of 
water. This is also Indicated by the temperature of the cloud layer ('\^30°C) . 
But we have neither photometric nor spectroscopic proof of the aqueous nature 
of the cloud layer on Venus . 

Motions in the lower atmosphere of Venus where no instruments have yet 
reached are completely unknown, as are the thermal conditions and Illumination. 
Ground observations are in no position to answer this question, so that we 
must place our hopes in future experiments with equipment launched into the 
atmosphere of Venus. 



29 



,»3sr7?^?fr 










tm-T"^: 






Theory, by the way, does 
permit answering one question, 
which had formerly caused much 
argument. This is the ability 
of the Venusian atmosphere by 

means of one of its effects, 

(2) 
the greenhouse effect , to 

maintain a temperature of the 
planet's surface and lower 
atmosphere at a level of 700° 
K or higher. Now the justifi- 
cations for the greenhouse 
effect on Venus have been 
found. As soon as the huge 
amount of carbon dioxide and 
a sufficiently large amount of 
water vapors on Venus were 
proven, its high absorption 
power in the near infrared 
band of the spectrum was in a 
position to retain the greater part of the natural radiation from the planet 
and in the same manner maintain the temperature at a high level (see below. 
Section 5) . There is no need for either a large influx of internal heat from 
the planet or even of strong volcanic processes (they are accompanied by the 
generation of large amounts of sulfur dioxide SO , but this gas has not been 
observed on Venus) . 




^^.fete^rf^^iifji i^t^^ianni gflrfirr ninf nti^r--- -ri r-- ^ "^-^fl-r^ 



Figure 10. The Earth at a distance of 70,000 
km. Photograph obtained by the Soviet un- 
manned spacecraft Zond-7. 



With respect to the atmosphere of Mars, for some time we have been 
confident of our knowledge, since this atmosphere is rarefied and we can 
look right through it. It is true that until quite recently the role of 



(2) 



For greater detail, see Chapter 5. 



30 



light scattering by aerosols was underestimated, and we have overestimated 
the amount of atmospheric pressure on the surface of Mars and assumed it to 
be equal to 80-100 mbar, whereas its correct value is near 10 mbar (probably 
less than more) . It is just such a value that is given by measurements of 
different CO absorption bands, carried out on the Earth, and also Investiga- /33 
tions of the damping of radio emission of the unmanned spacecraft Mariner (see 
below, Section 5) in going behind the planet Mars. The difficulties arising in 
interpreting the spectral and photometric measurements rest mainly on the 
impossibility of taking into account the role of aerosols in the scattering 
of light. It is quite probable that the atmosphere of Mars is significantly 
colder than its surface. This is indicated by the estimate of temperature 
from the structure of the atmospheric spectral bands on Mars and from the 
results of radioscopy of the atmosphere by radio waves. 

Cloud formations on Mars are an ordinary phenomenon, but quite variable. 
Here dust storms and haze are observed. As a rule, the Martian atmosphere 
strongly scatters violet rays, and when Mars is observed through blue or 
violet filters, very little can be seen. But a blue clearing sometimes 
exists in these rays also, and then the atmosphere of the planet is especially 
transparent. In its random nature, such a transparency was characteristic 
of the entire atmosphere of Mars at the time when Mariner-6 and Mariner-7, 
flying near it, photographed its surface. Recently the "violet clouds" on 
Mars have been found to be similar to terrestrial noctilucent clouds. But 
we should not be deluded by this comparison. Its cognitive value is not very 
great. It is sufficient to recall that arguments are still going on con- 
cerning the nature of terrestrial noctilucent clouds. 

As far as Jupiter's atmosphere is concerned, although for the past 
several decades there has been some information about it, much remains 
completely enigmatic. The bands visible on Jupiter, of course, are cloud 
formations, the nature of which can be hypothetically established based on 
theoretical arguments. The basic cloud layer consists probably of solid 
particles of ammonium hydrosulfide (NH.HS) and small drops of an ammonia 
solution in water (NH.OH) . The richness of the colors, mainly reds and 

31 




Figure 11. Photograph of Jupiter, taken 
on February 16, 1968 through a green 
light filter. 



oranges, is created by cyanides of 
HCN and C_N_, which by polymerizing 
and converting to the solid state, 
assume chemical stability. In the 
laboratory these intensely colored 
compounds are formed by electric 
discharge in a mixture of methane 
and ammonia (in the absence of 
oxygen) . Higher up, above the 
basic massive clouds, up to the 
troposphere, crystalline particles 
of solid ammonia are suspended 
which form a light haze. The haze /34 
is observed only by using specific 
methods, and is found to be a 
variable phenomenon. In particular, 
Jupiter has its own type of "polar 
caps" of these particles, whereas 
Saturn has none. 



Thus, in general, we can explain the diversity in colors and shades 
visible on Jupiter. In particular, the dark bands of Jupiter are not gaps 
in the cloud layer, but are simply clouds having a different composition. 
All of these are comparatively high formations at the level of which the 
pressure comprises several atmospheres (2-5 atm) , and the chemical composition 

of the atmosphere as determined from spectral observations is the following: 

(3) 
methane (about 100 m-atm) , ammonia (on the order of 10 m-atm) , hydrogen /35 

(85,000 m-atm). Based on theoretical arguments the atmosphere of Jupiter 

should have an abundance of helium (about 26 km-atm) , but it is not amenable 

to observations from Earth. These quantitative estimates are quite unreliable. 



(3) 



1 cm-atm characterizes the amount of gas in a column having a height 
2 



of 1 cm and an area of 1 cm at a pressure of 1 atm and a temperature of 0° C; 
1 m-atm = 100 cm-atm; 1 km-atm = 1000 m-atm. 

32 



since the role of multiple scattering, which certainly is effective in the 
atmosphere of Jupiter, is unknown. This is particularly indicated by the 
fact that absorption in the methane bands is not amplified toward the edge 
of Jupiter's disk, but rather is diminished. Therefore, the numbers given 
above in meters-atmospheres refer to the gas content in the atmosphere of 
Jupiter not only above the cloud layer, but inside this layer as well, along 
a complicated and intricate path of light quanta which are multiply scattered 
in the clouds. 

Bearing in mind the low temperature of the upper atmosphere of Jupiter, 
we have no right to expect indications of water vapors in its spectrum, but 
as to whether they do, in fact, exist in the lower atmosphere, which is 
warmer, is an important and interesting question, since this would incidentally 
solve the problem of the existence of oxygen on Jupiter. Free oxygen or the 
presence of a large amount of free hydrogen obviously does not exist. No less 
interesting would be the establishment of carbon dioxide in the atmosphere 
of Jupiter, which must also be destroyed by frost in the upper atmosphere. 

Temperature measurements in the infrared rays gave values of 150 and 128° 
K at wavelengths of A 20 y and X = 8-14 U, respectively. Radio measurements 
in the range A < 3 cm gave approximately the same values in the range of 
110-150° K. At the same time, the equilibrium temperature, that is, the 
temperatures at which the heat received from the Sun and the heat emitted by 
the planet into space are quantitatively equal, is 110° K for Jupiter — 
that is, significantly less than the measurements give. Consequently, the 
internal heat of the planet reaches the surface of Jupiter which we observed 
and increases the heat flux leaving it by no lesd than 20%. 

In measuring the emission from Jupiter in the radio band, there are 
indications that the temperature increases with depth, and the variable 
intensity of emission points to atmospheric activity. This is also in- 
dicated, although not explained, by the appearance of "hot shadows" — 
at a wavelength of X = 10 y an increase in temperature in the shadow cast, 
on the planet by its satellites. 

33 



A decisive event in observational astronomy is the obscuration by a /36 
planet during its travel across the sky of one of the stars of sufficiently 
bright to be observed at the time of extinction as it passes beyond the 
atmosphere of the planet approaching it. For the past ten years only three 
such cases have been registered: obscuration by Venus of Regulus in 1959, 
by Jupiter of a Aries in 1952 and by Neptune of a seventh magnitude star 
BD-17°4388 in 1968. The photometric observations of the star during ob- 
scuration make it possible to determine the altitude of the uniform atmosphere 

(4) 
H of the planet at various levels and then to find either molecular weight 

or temperature, if the other quantity is known . If the temperature value of 
100° K, which prevails in the upper layers of Jupiter's atmosphere Is proven, 
for which H = 8.3 km has been found, then the molecular weight of its upper 
atmosphere is near 3.8, which is similar to the molecular weight of helium 
(4.0), which has not been spectroscoplcally detected in the atmospheres of 
the planets. But hydrogen H„ (molecular weight p = 2) has been detected on 
Jupiter in huge amounts, while the heavier CH, and NH , on the other hand, have 
been found in relatively negligible amounts. Therefore, the molecular weight 
]i = 3.8 indicates that, in terms of volume, helium makes up quite a signifi- 
cant part of Jupiter's atmosphere; we mentioned this earlier. When our radar 
equipment is found to be adequate for locating Jupiter's satellites, radioscopy 
of its atmosphere will become a commonplace event, and will give much more 
information concerning the scale of altitudes, horizontal movements in it, 
and its dielectric properties. 

Jupiter seems to be the most enigmatic of the planets. These enigmas 
begin from its visible surface and extend both to the deepest and to the 
uppermost layers, its exosphere. 



The quantity H is also often called the "scale height", since it is 

the difference in altitudes corresponding to the decrease in atmospheric 

pressure by a factor of e (2.718...). 

(5) 

For greater detail, see Chapter 5. 

34 



The different angular rate of rotation of the various zones of Jupiter 
depending on the their distance from the planet's equator (equatorial 
acceleration) can be comprehended and probably theoretically Interpreted 
based on the fact that the planet's atmosphere is very large, its rotation 
is very rapid, and the centrifugal and Coriolis accelerations are high. 
Spectral observations have revealed a strange incongruity between the linear /37 
rotation velocity of the clouds and the gas component of Jupiter's atmosphere. 
Sometimes it seems that the ammonia and the methane do not participate in the 
planet's rotation; that is, the gas masses move counter to the rotation, which 
obviously may be accomplished only at a level other than the level of the 
clouds, and in any case, indicates a certain unusual type of atmospheric 
circulation. But such an exceptionally stable formation as the Red Spot also 
has its own special rotation period, so that this atmospheric formation moves 
relative to the surrounding atmospheric masses, which in the vicinity of the 
Red Spot have velocities up to 100 m/sec. There are indications that the 
atmospheric circulation takes place around it with a period of 12 days. 

This and many other factors indicate a tremendous atmospheric activity 
on Jupiter, but the nature of the activity is not clear. The role of the 
Sun in the thermal conditions of the planet even with a small penetration 
into the atmosphere of Jupiter is small — the heat flux from the Sun there 
is 27 times less than on Earth, and a significant part of it is reflected 
into interplanetary space. The rapid rotation makes the time variations in 
solar radiation insignificant during the day, and the small inclination of the 
planet's axis and the almost circular orbit of Jupiter makes the variations 
small during the year. We can understand the latitude distribution of the 
atmospheric processes, because of the latitude dependence of solar radiation 
and acceleration of gravity is constantly in operation on Jupiter . In 
addition, to the latitudinal heterogeneities there are considerable longitudi- 
nal heterogeneities. 

Deeper into the atmosphere of Jupiter, we encounter ever-increasing 
temperature and pressure. This latter may reach values at which H and He 



35 



are converted into the solid state; at various latitudes, such a conversion 
will take place at different depths, and there must not he any longitudinal 
variation here. Thus, the question arises as to whether those layers of the 
planet are chemically and physically uniform where the atmosphere loses its 
meaning . 

The theory which suggests a uniform composition, of course, does not 
agree with this concept. The mass, radius, and moment of inertia of Jupiter 
(and Saturn) indicate a low density of the planetary matter, that is, either /38 
a predominantly hydrogen composition (with helium admixture) or a high 
temperature in its interior, so that the elasticity of the gases successfully 
resists hydrostatic pressure. Here considerable convection may take place as 
well as an energy transport of heat to the outside, which is confirmed by 
observation only to a small degree. 

Another group of incomprehensible phenomena on Jupiter involves, on the 
other hand, its surface regions. As was said above, the brightness temperature 
of Jupiter at wavelengths of A < 3 cm corresponds to the temperature measured 
in the infrared region. Already at a wavelength of A = 10.3 cm the emission 
from Jupiter corresponds to a temperature of about 600° K; at A = 22 cm, 
3000° K; at A = 31 cm, 5500° K; and at A = 68 cm, 70,000° K; that is, these 
emissions are clearly of nonthermal origin and indicate the existence near 
Jupiter of a powerful magnetic field (many times stronger than the magnetic 
field of the Earth) and a belt of high-energy particles, similar to the 
radiation belt of the Earth. These particles move in the trap of the magnetic 
field and are de-excited by the mechanism of synchrotron radiation. The 
decimeter radio emission from Jupiter is partially polarized, which makes 
it possible to establish the direction of the planet's magnetic axis, that is 
Inclined from the axis of rotation by 10° . The polarization plane varies 
slightly with the period, equal to the period of rotation of Jupiter, and 
this reveals a misalignment of the axes. 

As mentioned earlier, the rotation period of Jupiter is not uniform for 
objects of the equatorial and the middle zones. For these, we must introduce 
36 



two systems of computing the longitudes: System I with a rotation period of 
9^50™30^. 003 and System II with a period of 9^55™40^.632. The fluctuations 
in the polarization plane of the decimeter emission from Jupiter take place 
at a period of 9 55 29 .37, that is, 11 seconds shorter than the rotation 
period of System II, which pertains to the middle latitudes. System III for 
computing the longitudes is determined in this way. 

The dimensions of the region of radio emission from Jupiter at decimeter 
wavelengths exceed its optical dimensions by far, reaching 2-3 planetary 
radii at the equatorial zone, although traces of this radiation may be noted 
also at a distance up to six radii. It is mainly this picture which serves 
as the basis for explaining the nonthermal emission from Jupiter by processes 
in the radiation belt. In the decimeter band, Jupiter is one of the most 
powerful sources of radio emission in the sky. 

But in the decameter band (X > 7m), Jupiter gives powerful bursts /39 
originating from discrete sources, also rotating with the period of System III . 
These bursts, 1-2 sec in duration or very short and on the order of 0.3 sec, 
have been known to radio physicists for some time, but only in 1955 were they 
linked to Jupiter. Even the Sun does not give such powerful impulses at 
decameter wavelengths. The dimensions of the sources, established inter- 
ferometrically, are 10-15 or 30-40,000 km, but apparently this value is 
strongly exaggerated by the scattering of radio waves in interplanetary space. 
It is remarkable that the decameter radiation from Jupiter depends on the 
position of the planet's magnetic axis relative to the observer from Earth; 
it is strongest when the northern magnetic band passes through the central 
meridian. It is even more remarkable that this radiation depends on the 
position of the nearest of the Galilean satellites of Jupiter — lo : its 
Intensity is maximal when the longitude of lo, computed from the superior 
geocentric conjunction, is equal to 90° or 240°. Jupiter's magnetosphere 
extends up to lo's orbit. Does lo affect the magnetosphere by a hypothetical 
magnetic tail or is it purely gravitational? This remains unclear. The 
source of decameter emission probably is different from the decimeter 



37 



emission. Just as in the case of bursts of radio emission from the Sun, 

the cause may lie in the plasma oscillations. But this is only a hypothesis. 

Thus, the radio emission, originating from the outermost layers of 
Jupiter's atmosphere, does not depend on the rotation of the visible cloud 
surface of the planet. But it is created in the magnetosphere , which is 
determined by the material carrier of the planet's magnetic field, connected 
with the body of the planet and with its inner regions. Perhaps the rotation 
period of System III is the true rotation period of the planet, and the 
rotation of Systems I and II reflects certain systematic motions of the gas 
mantle of Jupiter: for latitudes greater than 12°, at a velocity of 4 m/sec, 
and at the equator, up to 110 m/sec. 

After Jupiter, Saturn's atmosphere presents nothing new. The chemical 
composition is the same, only the presence of ammonia is uncertain. This is /40 
easy to understand since ammonia must be in the solid state at the lower 
temperature of Saturn. The temperatures of Saturn measured in the infrared 
band vary in a range from 85 to 125° K. The lower values are preferred, 
since they are confirmed by radio measurements: 97° K at A = 3.2 mm, and 
from 96 to 116° K at A = 8.6 mm. With increase in wavelength, the temperature 
grows; 190° K at X = 11.3 cm and about 300° K at A = 21.3 cm. This indicates 
a slow elevation in temperature with depth: short-wave radiation does not 
reach us from the greater depths. Here there is no similarity to the sharp 
increase in brightness temperature which was mentioned for Jupiter and 
interpreted by us as sjmchotron radiation in the magnetosphere. We know of 
no indications of a magnetic field on Saturn (polarization of the radio 
emission is not certain) . 

On the disk of Saturn the details observed are much smaller than those /41 
on Jupiter, probably because the clouds of Saturn consist of methane rather 
than of ammonia. Saturn's atmosphere is more extensive than that of Jupiter, 
and the differentiation in rotation velocity with latitude is stronger 
(lo'^14"' at the equator, and 10^^40™ at a latitude of 50°). 



38 










Figure 12. Photograph of Saturn and its rings. 



Uranus and Neptune 
continue the trend mentioned 
in the transition from 
Jupiter to Saturn: intensi- 
fication of the absorption 
bands of methane and hydrogen. 
But the existing quantitative 
estimates of the amount of 
methane (150 km-atm on Uranus, 
and 250 km-atm on Neptune) 
are highly unreliable and may 
be in error by an order of 
magnitude. The brightness 
temperature of Uranus was 
measured with a very high 



error: T = 100° + 35° K for A = 6 cm and T = 128° + 40° K for A = 11.3 cm. 
We do not know to which level this pertains. If the heating were only from 
the Sun, the equilibrium temperature would be only 60° K. It may be, just as 
on Jupiter, that a notable heat flux comes from the interior of the planet. 
Uranus and Neptune possess the highest reflectivity of any of the planets of 
the solar system (albedo of 0.93 and 0.84, respectively). The brightness 
temperature of Neptune is found from radio observations to equal 180° + 40° K 
at A = 1.2 cm and 115° + 36° K at A = 3.12 cm. Photometric observations 
show a temperature of 110°-130° K for sufficiently high layers of the 
atmosphere, and a very slow drop in density with altitude; the altitude of 
the uniform atmosphere is H = 50 km, which may be explained by the rich 
amount of hydrogen. 



Pluto, the last member of our planetary system, has remained completely 
unstudied, but it is in no way similar to the giant planets; even its 
rotation is slow, with a period of 6.39 days. Its dimensions are known 
with a low degree of reliability, and, therefore, the low value of the 
albedo (0.14) derived from its visible brightness is also uncertain. If we 
accept this, then we must assume that Pluto's atmosphere is insignificant. 

39 



We know of 32 planetary satellites in the solar system. Their dimensions 
are quite different — from several kilometers (Deimos, satellite of Mars) 
to several thousands of kilometers (the Moon, the Galilean satellites of 
Jupiter, Titan — satellite of Saturn, Triton — satellite of Neptune), but 
only for Titan has an atmosphere of methane been reliably observed. 



40 



^' INTERNAL STRUCTURE OF THE PLANETS 

The internal structure of the planets cannot be a topic for direct ob- /42 
servations. Only certain integral characteristics of a planet are functions 
of its internal structure, but the functional dependence is not unique, so 
that the investigator can only construct a guess as to a planet's structure, 
without pretending to have accurate knowledge. Knowledge of the temperature, 
density, chemical composition, and existence of phase modifications of matter 
as a function of depth could give a great deal of information for solving the 
problem of a planet's formation, be it cooling of the primitive mass ejected 
from the Sun or accretion by the planetary nucleus of the matter surrounding 
it, or condensation of matter in a constringent gas-dust cloud in the presence 
of the Sun. The preference for one of these three possibilities would open 
the way to solving still another question — the frequency of the process of 
forming planetary systems in the Galaxy. In addition, the question of the 
primary chemical composition of matter producing the solar system would be 
explained. 

Unfortunately, we are still quite far from answering these questions. 
Here we can see the vast scope of theory, but not experiments. 

In addition to mass, radius, and mean density following from it, we 
still know only the moment of inertia of the planet among the integral 
characteristics. The surface temperature in no way determines the distribu- 
tion of temperature in the depths. The existence or the absence of a 
magnetic field on a planet would give certain indications on the internal 
structure of a planet if we had a reliable theory for the onset of a planet's 
magnetic field, even of our own Earth. 

Even living on Earth, we know little about its internal structure. 
Concepts exist in geophysics about this that are mutually contradictory and 
estimates of the mean temperature differ by factors of two-three. Abrupt 
changes in density at the boundaries of various zones inside the Earth, 

41 



established by seismic observations, are Interpreted by some authors as 
signs of a varying chemical composition and by others as the result of 
change in the phase state of matter. 

But if we do not attempt to explain the details, knowledge of the mean /43 

density of a planet as a whole — that is, the arithmetic result of dividing 

the planetary mass by its volume — results in a topic for discussion. Thus, 

for example, planets of the Earth group located inside the ring of asteroids, 

that is. Mercury, Venus, Earth, and Mars, possess a high mean density of 4-6 

3 
g/cm , whereas the giant planets, Jupiter, Saturn, Uranus, and Neptune, have 

a density significantly smaller. Jupiter and Saturn have a mean density 

less than the gaseous Sun. The mean density of Saturn is half that of the 

Sun. 

One assumption stipulates that there is a substantially different 
chemical composition and different types of structures for certain groups of 
planets. The inner planets have a higher density which is naturally 
attributed to the presence in their interiors of iron, a heavy element 
which is widely distributed throughout the universe. The lower density of 
the giant planets can be understood if we assume their chemical composition 
to be near that of the Sun and the stars, where the lightest elements, 
hydrogen and helium, predominate. 

Prior to 1920, it was assumed that Jupiter and Saturn are uncooled 
planets because of their low density, fast surface variability, and the 
existence on Jupiter of the Red Spot. They were considered as a peculiar 
type of small sun, not so hot as the Sun, but nevertheless, in the "fire- 
liquid" phase. Therefore, publication of the results of the first measurements 
of the thermal fluxes from these planets, indicating a very low temperature, 
came as a shock. Theory helped recover from the shock. Namely, the theore- 
tical discussions did not include such small (in comparison with the Sun) 
bodies in the self-luminous category, since at a high surface temperature 
they would have to "burn up" their small reserves of heat in a short period. 
Then they were assumed to all be completely cold bodies. This also was 

42 



inaccurate. Let us recall that the temperature measurements of Venus in 

the infrared band gave a value of 240° K, and in the decimeter wavelengths 

it indicates a temperature of up to 700° K. The first value refers to the 

upper atmosphere, the upper boundary of the clouds, and the second to the 

planet's surface. Between one and the other level, the temperature drops in 

a regular fashion as a result of the fact that absorption of its thermal /44 

emission takes place in the planet's atmosphere. In the cloud layer there 

is also a strong scattering. The atmosphere itself is sufficiently extensive to 

accommodate the processes of damping of the outgoing radiation. 

The same factors must operate also in the huge atmospheres of the outer 
planets, Jupiter, Saturn, Uranus, and Neptune, so that in their depths the 
temperatures must reach thousands of degrees. We have seen signs of internal 
heat outflow from these planets, first of all in that the temperature 
measured in them is higher than equilibrium temperature, and secondly, during 
the measurements at the longer waves of the radio band the observed tempera- 
ture was higher. 

Another integral characteristic of the planet, its moment of inertia, 
is determined from the motion of the line of nodes or the line of apsides 
of the orbits of the satellites or from the flattening of the planet if the 
planet is in hydrostatic equilibrium. The theory has been well developed 
only for slow rotation. The ratio of the moment of inertia I to the moment 
of inertia ^/a 3Ri?' of an equally large globe, the entire mass of which is 
distributed along the surface, is equal to 3/5 for a uniform sphere, and to 
zero for a body with a mass concentrated at the center. On Earth and Mars, 
the ratio I'.^^U^R^) is equal to 0,50 and 0.58, respectively, thus indi- 
cating a sufficiently high uniformity, and for the outer planets it is shifted 



The line of nodes is the line of intersection of the orbital plane 
of the satellite with the orbital plane of the planet itself around the Sun 
or (in the case of artificial satellites) with the equatorial plane of the 
planet. The line of apsides is the major axis of the orbital ellipse, con- 
necting the nearest and the farthest position of the satellite relative to 
the planet. 

43 



toward 0.39-0.31, that is, toward a greater heterogeneity. The theory which 
takes into account the rapid rotation of Jupiter and Saturn indicates large 
mean densities of 2.7 and 1.7, respectively. The purely hydrogen-helium 
composition of these planets would not be allowable if it had not been for 
the discovery (theoretically) of a metallic modification of hydrogen at a 

pressure of 5,000,000 atm. At 30,000,000 atmospheres, the density of 

3 3 

hydrogen equals 3.1 g/cm , and of helium — 7.6 g/cm . 

For these two planets, acceptable models are found with a relative 
amount of hydrogen of 80 and 68%. The models which agree with the observed /45 
values of I have been found for Jupiter and Saturn also, with a hydrogen 

content of 78 and 63%, respectively. At the center of these planets, where 

3 3 

the theoretically computed density reaches 31 g/cm and 16 g/cm , helium 

sharply predominates. 

We have cited these low-reliability numerical characteristics in order 
that we might give some idea as to what the internal structure of the giant 
planets may be ; this is derived on the basis of a comparatively simple 
theory. Even for Uranus and Neptune, which have a comparatively high mean 
density of 1.47 and 1.88, respectively (versus 1.30 and 0.71 for Jupiter 
and Saturn), with relatively small dimensions, the hydrogen-helium composition 
does not fit. We must introduce into the examination the ice of water, 
methane, ammonia, hydrogen sulfide, oxides of metals and even metals. But 
by varying their content, we can obtain all the integral characteristics. 

It would be very important to know how far the atmosphere of Jupiter 
and Saturn extends, if a liquid layer exists at the bottom of the atmosphere, 
or if the atmosphere and the solid surface come into contact. The theory 
assumes that both atmospheres are quite extensive, and comprise, respectively, 
20 and 50% of the mass of the entire planet. Then at their bases there must 
be such high pressures that a liquid phase is Impossible. 

Furthermore, as we have seen in the previous chapter, Jupiter and, to 
a lesser degree, Saturn, have large heterogeneities under the cloud layer; 

44 



otherwise we would not observe the diversity in forms of the cloud surface 
of these planets. We can, therefore, pose the question as to the internal 
activity of Jupiter and Saturn, similar to the manner in which we pose the 
question of solar activity. 

The inner planets, of course, are more complex to comprehend. Although 
it is easier to make an analogy with Earth here, the indeterminancy of the 
answer is not diminished, and, in particular, it remains debatable as to 
whether one or another planet possesses a core. One of the most popular 
theories of the Earth's magnetism relates the existence of a magnetic field 
with the dynamo mechanism in a liquid conducting core where convection takes 
place. At the present time, the direct contacts of the unmanned space 
stations with the Moon, Venus, and Mars have shown that none of these 
celestial bodies has any notable magnetic field. 

The existence of a radiation belt on Jupiter proves the existence of a 746 
magnetic field on it. As we have seen above, Saturn has no clear indications 
of a radiation belt. Nothing is known about this on Uranus and Neptune. 
Thus, of all the planets of the solar system, only on Earth and Jupiter can 
we state with confidence that a magnetic field exists and possibly only on 
these two planets are there liquid cores. We cannot exclude the possibility 
that Jupiter has a magnetic, productive core which reaches the atmosphere 
and that certain of its atmospheric formations, such as the Red Spot, have 
a connection with the magnetosphere. 

The difficulties entailed in a theoretical investigation of the internal 
structure of the planets follow not only from the poor knowledge (or lack of 
knowledge) of the phase states of the various materials at high pressures or 
temperatures of several thousands of degrees — which are, apparently, 
typical for the interiors of the planets — but also from the incompleteness 
of our concepts concerning the transport of heat inside the planet. Thus, 
assuming that in the formation of the planet radioactive decay heated the 
interior of Jupiter, we can find a temperature differential of 10,000° 
between its center and surface, if the mechanism of thermal conductivity 

45 



operates. It is much smaller if, to the thermal conductivity, we add 
transport by conduction and radiation. But the theory of radiation trans- 
port inside a planet has not been completely developed. 

The appropriateness of one or another model of the internal structure 
of a planet is examined not only from its integral characteristics, but also 
from the agreement of the model with our concepts concerning the past 
history of the planet, and this in turn depends on the way in which the 
solar system was formed. At the present time, it is most probable that the 
planets were formed by condensation of matter from a gas-dust cloud, 
separately into a central star and separately into planets. Before the 
large planets were formed, small bodies — planetesimals — were formed, 
which were then combined into larger ones. Here the kinetic energy, due to 
inelastic collisions was converted into thermal energy. The newly formed 
planet was warmed up. Radioactive decay was another source of internal heat, 
which was no less if no more effective. The planetary matter was converted 
from the crystal state either into a melted state if the high pressure did not 
prevent this or, remaining solid, changed into another modification. At /47 
sufficient pressure, it was metallized, that is, under the influence of 
pressure the bound electrons of the atoms and molecules passed into the zone 
of conductivity, and this substantially increased the thermal conductivity 
of the matter. But increase in thermal conductivity increases the transport 
of heat from the depths of the planet to the outside. If these materials, 
for example, silicates, are not metallized and remain crystalline, then 
their thermal conductivity drops with elevation in temperature, thus facili- 
tating heating of the planet. In addition to the conductivity, the heat is 
transported by the silicates via radiative transport. 

As we see, the picture is rather complex, and if we do not wish to end 
in a controversy, all the above processes must agree with our concepts on 
the age of the solar system. Judging from the age of the Earth, the 
formation of the solar system took place about six billion years ago and 
already during the first 200 million years the planets were heated approxi- 
mately as in our time. Their further thermal history is determined by the 

46 



radioactive decay of their matter. The mass of the planet determines the 
content of radioactive materials in absolute numbers. 

On Earth only silicate rocks possess radioactivity; they are more 
abundant in the crust than in the mantle. Rocks containing iron are free 
of radioactivity. In the giant planets with their overwhelming amount of 
light elements, the radioactivity is weak, but the reserves of heat, 
accumulated in the formation of the planet (due to the energy potential) are 
so high that for the entire time of their existence — for example, Jupiter — 
the internal temperature has been lowered by no more than 1000° K. 

We might think that the planets of the Earth group have an internal 

structure similar to that of the Earth. We assume its crust has a thickness 

3 
of 18-20 km with a mean density of about 2.5 g/cm . Beneath it is the 

mantle, in which the density increases with depth, first rapidly and then 

slowly. The core is even deeper. 

The physical heterogeneity of the Earth's structure is indicated by its 
elastic properties as they appear from the propagation of seismic waves. 
At a depth of more than 2900 km, no transverse elastic oscillations are 
propagated, and a sudden change takes place in the properties with increase 
in density. This change can be attributed to change in the chemical composi- 748 
tion, for example, to the fact that the heavier elements are ejected through 
the viscous magma of the mantle nearer the center where they accumulate, 
forming a heavy core. But it is possible, using the concept of the uniformity 
of the Earth's chemical composition, to explain the abrupt change in elastic 
properties and density by the conversion of olivine rocks (a mixture of mag- 
nesium and iron orthosilicates) under the influence of high pressure from 
the ordinary crystalline phase state into a metallized state. This transition 
changes the olivine into a liquid state of high density, characteristic of the 
Earth's core, in which about one third of the Earth's mass is contained. 
But at the very center there is still another core in which about 8% of the 
core's mass is located, or altogether only 2% of the Earth's mass. This 
core consists of iron and nickel. It is solid, unlike the larger core. 

47 



Thus, the Earth, used as an example, has a multilayer structure, which may 
or may not be applicable for explaining the structure of the other planets 
of the Earth group. 

Mercury, with its small mass, has the greatest density in the solar 
system. In it is either a small iron core, surrounded by silicates with an 
iron inclusion, or iron and nickel are distributed evBryvrh.e.re with the 
silicates. But they are not molten due to the sparsity of radioactive 
elements. For the last two billion years. Mercury has been cooling off. 

Venus, which is similar to the Earth in mass and dimensions, certainly 
has an iron core and a core of metallized silicates. The latter contains 
about one fourth of the entire mass of the planet. At its boundary a 
pressure of 1.5 million atmospheres is reached, which makes metallization 
possible. The core may be molten, but a crust is located only at the surface. 

Finally, Mars, probably has a small iron core (7% of the mass) and a 
very thin crust. 

The specific difficulty in constructing models of the inner planets 
lies in the impossibility of controlling the (other than the Earth) magnitude 
of their moment of inertia. For Venus and Mercury, which have no satellites 
and with practically a spherical shape, which is natural with a very slow 
rotation, the moment of inertia cannot be determined. A flattening is 
observed on Mars which significantly exceeds the theoretically expected value /49 
from the most widely accepted assumptions on the distribution of masses. It 
may be that the observations of the shape of Mars' disk involve some systematic 
error. In passing, we should mention that the flattening of the Earth also 
is greater than that which would be expected from its rotation velocity, if 
our planet were in hydrostatic equilibrium. 

Directly related to this subject of the internal structure of the planets 
of the Earth group is the question of the formation of their surfaces. We 
have already mentioned this at the beginning, in connection with the 

48 




Figure 13. Rills on the Moon. The so- 
called "Cobra's Head" in Schroter's 
Valley. The picture was taken by the 
apparatus on the Lunar Orbiter. Frame 
size 4 X 4 km. 



seas appear as the result of lava eruptions on 
for assuming molten rock on the Moon, tectonic 
processes in the crust, and volcanic processes 



description of the lunar and 
Martian landscapes; only for 
these two objects is the land- 
scape known to us sufficiently 
well. We have also turned our 
attention to the fact that in 
the formation of the lunar 
surface both internal and 
external factors played a role. 
If in the majority of cases it 
is necessary to assume an ex- 
ternal impact of large outside 
masses for the formation of the /50 
circular mountains , then for the 
formation of mountain ranges 
on the moon, tectonic processes 
are essential that are asso- 
ciated with the elastic tension 
in the crust, and the lunar 
a huge scale. Is there a basis 
movements based on the thermal 
of small and large scale? 



This last question sounds somewhat rhetorical after N. A. Kozyrev 
observed, if not direct volcanic damage, then an abundant generation of 
gases accompanying the damage inside the lunar crater Alphonsus. But what 
does the theory of the internal structure of the planets say on this score? 

We know the mass, radius and moments of inertia of the Moon with respect 
to the different axes, sufficiently well to construct a model of the Moon 
with confidence. The lunar mass is extremely small, and, therefore, the 
pressure at its depths nowhere reaches such values that metallization of the 
silicates could take place, so that the Moon has no core. The lunar mantle 
contains a sufficient amount of radioactive elements which heat it up before 



49 



melting, which takes place at a depth of about 300-400 km. In any case radio 
measurements at various wavelengths of the heat flux leaving the Moon clearly 
indicate a rather rapid increase in temperature with depth, caused probably 
by a high concentration (four times higher than on Earth) of radioactive 
elements near the lunar surface. 

Individual sites of the lunar surface are found to be much hotter than 
their surroundings. For example, such are the numerous craters and cirques of 
large and small dimensions such as Tycho, Copernicus, Kepler, Hosting C, and 
several of the seas such as Mare Tranquillitatis, Mare Serenitatis,Mare Humor- 
um, which appear especially in relief under infrared observations during total 
lunar eclipses. These "hot points" can be easily explained by the fact that 
they are composed of rocks with high thermal conductivity, which easily 
transport the internal heat to the lunar surface. But this may also be heat 
which is accumulated by the upper surface layers during the long lunar day. 
On the other hand, recently a formation was detected which extended into a 
long band along the western boundary of Mare Humorum (toward the south from 
the crater Gassendl) , which is constantly hotter than the surrounding sites 
outside the eclipse, at the height of the lunar day. Here we encounter a /51 
nonequilibrium process, the cause of which is the real transport of heat along 
paths created by the structure of the lunar crust at a given site (fractures, 
faults. . .) . 

Thus, theory and observation fully indicate the existence on the Moon 
of high-temperature zones capable of producing tectonic processes and vol- 
canic phenomena, and in the same manner help us understand the processes 
which take place on the surface of the Moon and to understand how the various 
details of the lunar landscape were formed. An interesting and important 
discovery in this respect in recent years was the discovery beneath the lunar 
seas of heavy masses, called mass-concentrations. The mass-concentrations 
were found to be anomalies in the motion of the artificial lunar satellites. 
They are rather numerous, but exist only beneath the seas, having a regular 
shape. We might think that these are residues of especially large planetesi- 
mals which pierced the crust of the Moon when they fell and produced vast 

50 



lava eruptions. The masses of the mass-concentrations comprise 10 -10 of 
the lunar mass. 

Other explanations also exist for the mass-concentrations, for example, 
as formations of hardened lava of high density which, after impact of the 
planetesimals, were extruded upward and formed huge formations, heavier than 
the surrounding continental rocks. Due to its large specific weight, such a 
formation even with a smaller expanse in depth is capable of rendering the 
same pressure on the upper boundary of the plastic mantle as the more 
extensive, but lighter continental and subcontinental formations. (Herein, 
as we know, lies the hypothesis of Isostasy first expressed with respect to 
the Earth more than 100 years ago) . In this explanation there is no need to 
attribute to the impacted planetesimal an excessively high density, which is 
only slightly probable since planetesimals of iron-nickel composition could 
hardly ever have existed. No matter what the case may be, the existence of 
large heavy heterogeneities under the surface of the Moon indicates that the 
Moon possesses a sufficiently thick crust above the magnetic mantle. 

The completely external formation — the rings of Saturn — we shall 
examine in the chapter on the internal structure of planets, because it has 
nothing in common in its nature with the surface of Saturn or its atmosphere. /52 
On the contrary, it may be explained as a relict phenomenon, indicating the 
initial conditions which accompanied the formation of the planets four to 
six billions years ago. 

From the time, more than 100 years ago, when Maxwell theoretically 
showed that the rings of Saturn cannot be integral, solid formations, and 
Belopol'skiy proved this experimentally by spectral observations, there has 
been no lack of explanations for the nature of the rings, mainly on the 
basis of their photometric study, during a change in the position of the 
rings relative to the Earth and the Sun. It was established that in the 
reflection of solar light the most important role is played by the mutual 
eclipse of the Individual blocks comprising the rings. But what are the 
dimensions of these blocks? Unfortunately, the opinions of theorists 

51 



disagreed, and even now some cite proofs that the rings consist of fine 
particles with dimensions in microns, whereas others speak of a conglomerate 
of blocks, up to two meters in cross section and smaller fragments (on the 
order of centimeters and less). Probably the truth lies with the latter. 
As far as the thickness of the rings is concerned, it can hardly exceed 3 km, 
since from the myriad of "satellites" of Saturn forming the rings, only those 
have been left intact which moved in the equatorial plane of the planet. 

It is very difficult to establish the chemical composition of the blocks. 
The spectrum of the rings in the infrared band reveals, as in the Martian 
polar cap, absorption bands that are characteristic of ice or hoarfrost. As 
to whether ice is found only on the surface of the blocks, or the blocks as 
a whole consist of ice, as yet is unknown. 



52 



5. INVESTIGATION PROCEDURES AND POINTS OF APPLICATION 

Radar observation of the planets . Among the investigation methods and /53 

their practical utilization, the richest possibilities are afforded by radar 

if it can be used effectively with respect to Jupiter and at the distance of 

this planet have a resolving power of even 1000 km, which corresponds to about 

1/3 second of arc. At the decameter wavelengths, a mirror (or complex group 

of components) would be required for this with a diameter greater than 

10,000 kml In the centimeter band the necessary dimensions of the mirror 

3 
would be 10 times smaller, that is, 10 km (at a wavelength of A = 1.7 cm). 

The effective wavelength might be decreased another factor of 10, and then 
the dimensions of the mirror would become realistic. But the problem of 
radar in the future will consist of analyzing the planetary surfaces with the 
aid of radio waves where optical means cannot penetrate the atmosphere of a 
planet and its clouds. For this, the millimeter waves are not suitable, 
since they are absorbed in the majority of planetary atmospheres and es- 
pecially in water vapors. The decimeter waves apparently encounter a barrier 
In the ionospheres of the planets if these latter are sufficiently dense and 
it is these which must undoubtedly be used for scanning Jupiter. 

Fortunately, contemporary powerful computer technology permits increasing 
the resolving power of our telescopes without resorting to huge mirrors, but 
by using an ingenious combination of mirrors of smaller dimensions and 
mathematical analysis of the incoming radio signal. It is true that the 
quality of the impulse returning after reflection is decreased (signal to 
noise ratio) but the information obtained is, nevertheless, quite substantial. 
An example is the reproduction shown on Figure 8 of the radar photograph of 
the region of the region of the Moon around the crater Tycho. It was obtained 
with the aid of a mirror having a diameter of 37 m at a wavelength of 3.8 cm, 
by Lincoln Laboratory in the USA. It shows the reflectivity of the lunar 
surface with a resolution of about 1 km. In order to obtain a resolution 
with one antenna, a mirror with a diameter of 18 km would be required I 

53 




The radar method of studying the 
surface of planets and their rotation 
takes advantage of the fact that the 
impulse reflected from the planet 
carries in itself information of three /54 
types: geometric (concerning distance), 
kinematic (concerning the approach or 
recession velocity) , and physical 
(concerning the reflectivity of the 

Figure 14. Schematic of radar probe site of reflection) . The first type 

of a planet (see text). . .^ ^ . , . ^ . , 

xs manxfested xn the txme of arrxval 

of the reflected signal, the second — 

in the frequency of reflection of the signal, or more precisely, by the 

frequency shift relative to the transmitted signal, and the third — in the 

strength of the returned signal. Turning to Figure 14, we can see that 

circles on the sphere of the planet, having as a common center that point of 

the planet (subradar point) , for which the Earth is located at zenith, are 

the geometric locus of the same lag in the reflected impulse. Let us select 

the plane XOZ, comprising the axis of rotation of the planet OX and the 

direction to the Earth OZ. Then the intersection of the surface of the planet 

with the plane parallel to the plane XOZ will be the geometric locus of the 

points having the same projection of velocity along the line of sight OZ 

during rotation of the planet. According to the Doppler-Flzeau principle, it 

gives the same frequency shift of the reflected signal with respect to the 

frequency of the signal sent. If we expand the reflected signal according to 

frequency (under the condition that the transmitted Impulse is strictly 

monochromatic) , then this will be equivalent to scanning the disk of the 

planet with a narrow slit. The Intensity of the signal with a given deviation 

Av from the frequency v of the transmitted signal characterizes the amount /55 

of energy reflected in a given band expressed on the disk by the "Interval of 

frequencies" Av , Av , . . . (see Figure 14). With a combined analysis of the 

frequency shift and the lag time of the reflected signal, we can even localize 

those sites on the planet's disk where an increased or diminished intensity 



54 



of reflection is observed, although it is true in the general case that the 
solution is ambiguous. 

At first glance, it seems that in the kinematic phenomena observed by 
the Doppler shift, nothing changes if the figure of the planet rotates with 
its axis of rotation around the line of sight on Figure 14. Such, in fact, 
is the case in observing the rotation of stars. We cannot determine the 
position of the axis of rotation of a star on the plane of a figure, per- 
pendicular to the line of sight, because the position of the terrestrial 
observer relative to the star remains practically constant (in the framework 
of the annual parallax of the star). A planet is another matter. The 
terrestrial observer with his radar equipment continuously changes his 
position relative to the axis of rotation of the planet, and the observed 
rotation is the sum of the axial and orbital rotations of the Earth and the 
planet. All these motions are known in advance, other than the axial 
rotation, and may be taken into account in advance. But since their sum 
vector constantly changes its position in space relative to the vector of 
axial rotation of the planet, the position of the latter may be derived from 
observations if they are continued for a sufficiently long period of time. 

The next example, pertaining to astronomers, will explain the matter. 
It is known that in opposition the upper planet moves with a retrograde 
motion most rapidly. Thus, Mars, observed from the Earth, moves during this 
time on a background of stars in the direction of diurnal rotation of the 
celestial arc. For the observer on Mars, during this time. Earth would seem 
to be rotating the most rapidly, and if the direction of the Earth's rotation 
were retrograde, during the time of the opposition of Mars, it would appear 
to the Martian observer to be the slowest. But this situation is fully 
reproducible also for the Earth observer when he observes Venus during the 
time of its inferior conjunction. Radar observations have shown that the 
width of the signal reflected by Venus is lowest in frequency rather than 
greatest at the moment of inferior conjunction. Hence, it follows that the /56 
rotation of Venus is retrograde, and the width of the signal gives a linear 



55 



II I iiniiBiiiiiiii I Hill I 




7.II.W6B 

C'EOO 

Z9.ri.WBi\ 

w 

X 



Figure 15. Comparison of profiles of 
radar signals reflected from Venus 
at a wavelength of 39 cm in two 
inferior conjunctions of the planet 
in January-February 1966 and in 
June 1964. The repetition of de- 
tails with respect to their 
reflectivity can be seen. 



rotation velocity for Venus at the 
equator, whence the period of rotation 
is derived. Finally, the law governing 
the change in the signal width with 
time establishes the orientation of 
the axis of rotation in space. 

The rotation period of Venus is 
most precisely derived by comparing 
the relationship of the frequency 
profiles of the reflected signals 
during the times of the different 
inferior conjunctions. One or another 
detail of this profile is repeated 
during the time of subsequent conjunc- 
tions. Its appearance at one and the 
same place of the profile indicates 
that a complete number of synodic 
(that is, relative to the Earth) 
periods of rotation of Venus has taken 



place. The transition from the synodic period S to the stellar period P is 

given by the formula cited (for circular orbits) by Copernicus : 151 

B ^ P S ' 

where E is the period of rotation of the Earth around the Sun. If the rotation 
of Venus were forward, then a minus sign would be placed in front of 1/P. It 
is natural that S must be taken in absolute value. 

The signal transmitted by radar has circular polarization. After specular 
reflection from sufficiently large details on the surface of a planet, it 
returns to Earth still polarized in the same manner, but opposed to the 
direction of rotation. A sufficiently rough landscape makes possible a 
specular reflection even from those places on the planet's disk which are 



56 



distant from the center all the way up to the limb Itself. On the other 
hand, the planet with a smooth surface gives a polarized reflection only 
from the central parts of the disk. Its effective cross section is greatly 
reduced, and for radar probes of the planet a more powerful impulse must 
be used. 

If the reflecting surface has numerous irregularities, the radius of 
curvature of which is less than the wavelength of the incident signal, 
polarizations in the inverse direction do not set in, and the reflected 
signal retains the direction of the circular polarization of the Incident 
signal. This part of the reflected signal is called its depolarized com- 
ponent, which may be the subject of a special Investigation when the signal 
arrives at the receiving antenna. In summation, radar permits investigating 
separately the polarized and unpolarized components of the reflected radia- 
tion, and from this the structure of the planet's surface can be judged. 
The coefficient of reflection during normal incidence makes it possible to 
find the dielectric constant of the surface materials, that is, their 
physical characteristics. 

Let us note finally that the possible rotation of the plane of polari- 
zation during the propagation of radar Impulses permits investigating the 
electrical state of the Interplanetary and circumplanetary plasma, and also 
the magnetic field around the planet on the basis of the Faraday effect. 

Thus, the greatest information Is contained In radar-reflected signals, 
which allows us to discover many facts that had previously been inaccessible. 
Earlier we mentioned a number of such facts about Venus, which is covered /58 
with a dense cloud layer. The large amount of Information reflects the 
scope of the investigation method. 

Radar gives the hope of collecting the most valuable information on the 
surface of Jupiter, to establish whether the surface adjacent to the at- 
mosphere is solid or liquid, to find the period of rotation of this surface, 
the degree of its geometric and physical heterogeneity, the relationship 

57 



between the surface and cloud formations, and many other facts which have 
been difficult to predict. 

But we encounter one basic difficulty in this approach, that is, the 
inadequate strength of the signal and the insufficient area of the antenna 
for sending and receiving the signal in the case of such a remote object 
as Jupiter, or such a small one as Mercury. The strength of the reflected 
signal, received by the antenna, is inversely proportional to the fourth 
power of the distance to the planet, and directly proportional only to the 
first power of the strength of the transmitted signal. The signal is 
damped in proportion to the square of the distance in the outgoing and 
incoming leg. Although, when the irradiator is placed at the focal point 
of the parabolic mirror, the beam of radio waves transmitted by the antenna 
must be parallel, diffraction makes it divergent within the limits of the 
angle of the directional diagram, which is always found to be greater than 
the angular diameter of the planet's disk. If the cross section increases 
In proportion to the square of the distance and becomes greater than its 
dimensions near the planet, then part of it will be wasted for the experiment. 
Therefore, the effectiveness of the radar experiment is higher, the narrower 
the directional diagram, and, therefore, is proportional to the square of 
the mirror's diameter. But this same mirror is in operation during the 
reception of the reflected signal, so that the success of the radar probe 
of the planets is defined as the fourth power of the diameter of the mirror. 
From Figure 16, which shows how many times the strength of the signal is 
attenuated travelling back and forth, it is clear that even the radar probe 
of Jupiter, if we expect reliable results from it, will require amplifying 
the strength of the transmitted impulse and increasing the dimensions of the 
antenna. In fact, at the present time the only fully reliable data, except 
for the Moon, are those of the inner planets, mainly Venus, and with the 
greatest success in the upper Interval indicated on Figure 16. The diffi- 
culties of radar scanning of Mercury have also been successfully overcome. /59 
For the last two oppositions. Mars has also become an obedient subject for 
radar Investigations. Jupiter requires improvement and intensification of 
technology. Although the data concerning Its radar scanning have been 

58 



■iniiiiiiiiiiiiiiii 



m 

300 
810 

'^KO 

^sso 

(U 

o 
•a 350 



—r\ — I — I I I Hit 



-1 1 I I I M I 



o[Sun] 



Mar 
(June 
(December 



CO 

I 380 




10^ 



f^[ Jupiter] - 



6 Icarus . 

(June 1968) Ganymede 
Eros o 1 Callis^to^ 
(May 1968^,^^/ Europa 



<u 



to 
u 

0) 

& 

o 

a 

e 

•H 

to 

OJ 
CO 
CO 

o 




iruranus 

I [Neptune] 
P'Titan; 






J" J" 



Figure 16. Attenuation of signal strength 
during its return to the radar equipment. 
Along the abscissa is plotted the time 
of the signal's motion at both ends, and 
along the ordinate is plotted, on the 
right, the attenuations in powers of ten, 
and on the left, in decibels. Each 
space object is represented by a line, 
encompassing the entire distance of the 
object from the Earth — from the nearest 
to the remotest. 



published in print, they have 
not been confirmed. Up to the 
present time, the growth in 
sensitivity of radar devices on 
Earth has been at a rate of 5.5 
dB (or 3.5 times) a year. It 
may be that a threshold corre- 
sponding to a loss of 390 db . 
will be reached in 1972. Then 
it will be possible to have 
accurate radar scanning of 
Jupiter and even its satellites. 
Radar scanning of Saturn will 
also be possible. 

Spectroscopy of the planets . 
Great possibilities for spectral 
analysis of the planetary at- 
mospheres are revealed by the 
method of Fourier-spectroscopy. 
The principles involved in this 
method can be understood if we 
recall the operating principles 
Light from the point source S 



1' 



of the Michelson interferometer (Figure 17) 

with the aid of the collimator lens L travels in a parallel beam to the 
separating plate P, mounted at an angle of 45°. Here the beam is split, 
being reflected from the translucent reflecting plane of the plate P, and 
partially travelling through it. The first beam encounters the mirror M, 
and the second — the mirror M„. Reflected from them, the light again 
encounters the plate P, being partially reflected from it, and partially 
passing through it, after which it is directed toward the lens L , which 
gathers both beams at the focal point F, where there may be an eye, a photo- 
plate or a photomultiplier . The beams travelling toward L„ interfere with 
one another. The focal point F will be "light" or "dark" depending on 



/60 



59 






^ 






3 AC, 




Figure 17. Schematic of the 
Mlchelson Interferometer. 



whether the path difference of the beams forms 
an even or odd number of half-waves of mono- 
chromatic light of a given wavelength. If the 
light Is not monochromatic, but "white", then 
It will always contain a wavelength A ' , which 
will give "light", and along with it X", which 
will result in a "dark" point A' and X" will 
differ to a lesser extent, the greater the 
path difference of the beams, reflected from 
M^ and M , because with a large path difference 
(due to the large number of half-waves con- 



tained in it) even for A' and A" quite close, 
there may be a difference up to a half-wave 

Now If the mirror M moves at a constant rate v from the middle position /61 
(for which the path difference is equal to zero) to the path difference t, 
then at the point F each wavelength will be modulated at a different fre- 
quency. The wavelength A = x will be modulated only one time, and the 

smallest A of the wavelengths transmitted — x/A times. In the general 
m m 

case, since the path x will be travelled for a time x/v, the frequency of 
modulation 

/ = t/A, : T/o = o/A, 



will also be different for the different wavelengths. At the same time the 
Intensity of the radiation modulated at a frequency f will be a direct 
function of the intensity of the radiation at the wavelength A = v/f . When 
the photocurrent is recorded from the photocell at the focal point F, then 
it expresses the effect of adding the emissions at all wavelengths of the 
examined Interval. This would be like noise containing a vibration in the 



Let us say the path difference Is 500A ' and then A" is determined 

A' A" 
from the equation 1000-r = 1001— r, which gives A' - A" = O.OOIA", whereas 

with a path difference of 50A', we find A' - A" = O.OIA". 



60 



wide frequency band. But at each moment their frequencies and their wave- 
lengths X participate in this noise and, moreover, at a different intensity, 
corresponding to the intensity in the spectrum. 

Since the examined noise is composed of many harmonic vibrations, all 
of its "vibration" for the period of the photocurrent recording (when the 
mirror of the interferometer moves) can be expanded into elementary harmonic 
functions, for example, according to cosines of all the frequencies of 
modulation — that is, it is subject to Fourier transformation. Such a 
possibility (theorists and experimenters) was predicted for optics even at 
the beginning of this century. But the practical mastering of this method 
became an actuality only in recent years after overcoming certain specific 
experimental difficulties, especially noticeable in astronomy, when the 
image of an object flickers strongly due to the instability of the atmosphere. 
Furthermore, the assistance of modern electronic computers has become possible, 
since without them the tremendous computational effort associated with 
Fourier transforms is simply inconceivable. It was further found that 
spectroscopy with the aid of an interferometer has the advantage of a 
greater luminosity versus the ordinary recording of the intensity of the 
spectrum. This is especially important in astronomy where the light sources 
to be investigated are very weak in comparison with those in the laboratory. 
With the appropriate precautions, the use of this method will significantly /62 
increase the accuracy of the measurements. Finally, the resolving power in 

Fourier spectroscopy may be significantly higher than in the classical 

(8) 
method . This is especially apparent in the infrared band, but not because 

the ordinary methods give a low resolving power in the spectrum (this is not 

so), but because, due to the low sensitivity of the infrared light receivers, 

the experimeter must register a wide band of the spectrum directly. Otherwise 



As we can see from the footnote on page 60, the resolution is ob- 
tained equal to 1/2t in the scale of wave numbers a (in cm ) . With the 

2 
aid of the relationship Aa/a = -AX/ A we find the expression AX = -X Act, which 

shows that the resolution is improved with decrease in wavelength. 



61 



his light receiver will simply not respond to the incoming luminous flux. 
The use of infrared receivers, which are distinguished by the fact that their 
noise, as a rule, does not depend on the strength of the signal, makes 
Fourier spectroscopy quite advantageous, especially when the problem is to 
obtain a high resolution in the spectrum. 

All these properties of Fourier spectroscopy are especially important 
in the investigation of the planets, since the majority of molecules com- 
prising planetary atmospheres are best seen in the infrared band with its 
rotational-vibrational spectra. 

All the small luminous fluxes reaching us from the celestial bodies 
including the planets, when our purpose is to carry out precise measurements 
of the intensity in the spectrum with a high resolving system, require a long 
recording time even with large telescopes and with the use of Fourier 
spectroscopy. Modern technical procedures — recording on punched tape or 
on magnetic tape and the subsequent transmission of this recording by 
telephone to a large computer center — make it possible with the least loss 
of effort and time to obtain a final result which even 15-20 years ago 
would have been impossible. Figure 18 shows a part of the spectrum of Venus, 
obtained in this manner by Konn and Mayar on July 3, 1966 on the 193-cm 
reflector of the observatory of Upper Province (France) in two approaches 
when Venus was near the meridian (Venera-1) and far from it (Venera-2) . The 
telluric lines, formed in the Earth's atmosphere, designated by the letter T, 
are much stronger in the second case. For comparison the spectrum of the Sun /64 
was recorded. All the lines, in the spectrum of Venus and absent in the 
spectrum of the Sun, belong to the weak band of carbon dioxide around X = 
= 2.2 y. The total observation time of the spectral region, which is twice 
as wide as shown here, was 27 hours. The time for transmitting the data to 
the computer center is somewhat less than this, but the computations themselves 
occupy 1-2 hours. 



62 




iSOO 



Z2ZV- 



wo 



ifSZO 



&ZfV 



ifSSBcM-- 



Figure 18. Part of the spectrum of Venus compared with the spectrum 
of the Sun in the range of 2.22-2.23 y. The telluric lines (formed 
in the atmosphere of the Earth) are denoted by the letter T. The 
lines forming in the solar atmosphere are denoted by the letter S. 
The others are formed in the atmosphere of Venus. The only differ- 
ence in the spectra from Venera-1 and Venera-2 is that the second 
was obtained at a lower position of Venus over the horizon. The 
majority of the lines in the spectrum of Venus belong to the weak 
band of carbon dioxide (CO.) . 



Radioscopy of a Planet's Atmosphere . The previously mentioned radioscopy 
of the atmosphere of a planet by the light of a star is a phenomenon that is 
both unusual and difficult to observe. 

This phenomenon does not depend on the will of man. Radioscopy of the 
atmosphere of a planet by radio waves from a spacecraft orbiting the planet 
is a much simpler affair (after the equipment reaches its target) , and it may 
be organized just like any other physical experiment. 

Let us acquaint ourselves with the principles of this experiment. 
Figure 19a, shows the passage of light beams through the atmosphere of a 
planet in simplified form, as though the atmosphere consisted of individual 
layers, at the boundary of which the light is refracted, so that the angle of 
refraction is less than the angle of Incidence if the light travels from a 
less dense layer to a more dense one. The opposite picture is observed when 
the light travels from the atmosphere. If we were to plot the refraction on 



63 



from star 




an infinitely large number of 
infinitely thin layers, the 
trajectory of the beam in the 
atmosphere would appear to be 
curvilinear in precise agreement 
with actuality. The described 
phenomenon is called atmospheric 
refraction in astronomy. As is 
obvious from the drawing, the 
initially parallel pencil of rays 
becomes divergent due to the 
refraction. 



to Earth 
c) 



Figure 19. Schematic of the radioscopy 
of the atmosphere of a planet by the 
light of a star (b) and by radio sig- 
nals from a spacecraft (c) . Refraction 
in the atmosphere of the planet (a) . 



Now let us look at Figure 
19b, where the obscuration of a 
planet by a star is shown. The 
planet is first affected by the 
star over its entire atmosphere. 
The parallel pencil of light from 
the star becomes divergent. When 
one of these rays, or more 
properly, a narrow pencil of rays, 
reaches the observer located at a 
distance L from the planet, the 
observer sees the star, but its brightness will be weakened, because as a 
result of refraction, the energy contained in the divergent pencil of rays 
is less than before refraction in the parallel beam of the same cross section. 
Such a refraction weakening is significantly greater than the weakening of 
light by absorption in the atmosphere. At first, when the star is behind the 
disk of the planet, light approaches the observer which has penetrated the 
more rarefied layers of the atmosphere, and then the denser ones. The star 
"darkens and goes out". This takes place more effectively, the greater the 
distance L of the observer from the planet. A precise formula shows that the 
weakening factor will be (1 + 2a)Lg) where 2a) is the angle at which the light 



/65 



/66 



64 



ray is deflected as a result of refraction when it passes through the 
atmosphere of the planet (horizontally, in the lowest part of its trajectory) , 
and 3 is the characteristic of change in the density of the atmosphere with 
altitude. An Increase of altitude of H = 1/3 km results in a density drop 
of a factor of e. In the formula for the damping, only u is a variable 
quantity, and the observer sees the progressive damping of the brightness of 
the star in proportion to the growth in the horizontal refraction w. Knowing 
very precisely the position of the planet and the star in space, and also 
the radius of the planet, we can compute at any given moment of observation 
how near the star approaches the planet's disk, and in the same manner we 
may always know the angle u). Consequently, from the observations we can 
determine the quantity 3 or its inverse scale of height H. But this quantity 
is associated with the characteristics of the atmosphere — its molecular 
weight VI » temperature T, and acceleration of the force of gravity g, by the 
simple formula 

where 9t is a universal gas constant. The quantity g is easy to compute. 
Consequently, after determining H from the observations, we can find the 
molecular weight y, if we know the temperature T. Conversely, we can 
determine T if we know y. 

Unfortunately, the temperature T is not constant in the atmospheres of 
the planets, although in the upper stratospheric layers, it is rather in- 
variable. The radii of the planets are known to us with an insufficiently 
high degree of accuracy, so that slight uncertainty remains in determining 
the level of the planet's atmosphere, to which these or other values of y or 
T pertain. The divergence may reach several scores of kilometers for Venus 
and hundreds of kilometers for Jupiter, but for an approximate determination 
of the physical parameters of the planets' atmospheres the method of radio- 
scopy is quite good. 



65 



One of its variations, radioscopy of the atmosphere by radio waves 
originating from a spacecraft is shown schematically on Figure 19c. It 
differs from the preceding case in that here we are studying the passage 
through the atmosphere of a beam of radio waves which diverge from the point /67 
source, the position of which M ,M„,... at different moments of time is known 
precisely . Figure 19c shows only those rays originating from the craft in 

positions M^ and M„, which have reached the observer on Earth. It seems that 

(9) 
here also refraction damping is also taking place, but in addition, there 

is still another effect, that is, change in the frequency or wavelength of 
the radio emission when it passes through the atmosphere. In general when 
the spacecraft travels the trajectory M ,M , . . . , the frequency of the radio 
signal varies as a result of the Doppler effect, because the rate of motion 
of the spacecraft and the angle between the line of sight and the direction 
of the motion both change. If the rate of motion in the projection on the 
line of sight is v, and the propagation rate of the radio waves is c, then 
the relative change Av in frequency v — that is, Av/v — is equal to the 
ratio v/c. But the rate propagation of the radio waves differs in a vacuum 
and in a refracting medium, whatever the atmosphere of the planet may be. 
Therefore, the signal may arrive on Earth with a phase which differs from 
that in the absence of an atmosphere. Taking into account all the sources 
of change in frequency and time of propagation on the path from the space- 
craft to the receiving antenna (including the role of the Earth's atmosphere) , 
we can compute for each moment the changes in the phase of the arriving 
signal, and after comparing them with the observed changes and after de- 
termining the divergence, we can attribute it to the effect of the planet's 
atmosphere. The divergence directly influences the change in the coefficient 
of refraction n, and this quantity — more precisely, its difference from 
unity, (n-1) — depends directly on the density of the atmosphere and its 
chemical composition. Thus, of course, after complicated treatment, we can 
obtain the density distribution with respect to altitude, and, hence, it is 



(9) 

The picture of the refraction of radio waves in the atmosphere, 

shown on Figure 19c, corresponds to short waves of the centimeter and 

decimeter bands. 

66 



easy to convert also to temperature. This method gives more precise results 
than measurement of the signal attenuation. 

In the experiment of Mariner-4 in its orhit near Mars, phase shifts were 
observed in the oscillations arriving both when the craft approached the 
planet's disk and when it emerged from it. Quantitatively they agreed well 
and during the time of the approach and emergence reached about 30 complete 

cycles of oscillations, which converting to the quantity (n-1) comprised a 

— fi 
factor of 3.6 X 10 . Hence, the value of the atmospheric density at the /68 

-5 3 
surface of the planet is about 1.5 x 10 g/cm (under certain assumptions 

concerning the chemical composition of the atmosphere) and the pressure varied 
between 4 and 6 millibars which is found to be in satisfactory agreement with 
the spectroscopic results. The scale height was found to be between 8 and 10 
km. Under various assumptions on the chemical composition, the temperature 
is found to vary from 170 to 180° K. The transmitter giving all this 
information operated at a frequency of 2297 MHz and had a power of only 10 
watts I Its distance from the Earth during this time was 216 million kilo- 
meters. 

In the experiment with Marlner-5 which completed flight around Venus 
with a transmitter frequency of 2297 MHz, the phase shift reached 140 cycles, 
and the changes in (n-1) comprised from 15 x 10 to 1464 x 10 for dis- 
tances from 6123 to 6088 km from the investigated atmospheric layer to the 
center of the planet. But what altitude above the level of the surface do 
these distances represent? For an answer to this question, we must know 
the radius of the planet's surface. Visual observations cannot give this 
quantity for Venus, — it is determined only from radio observations and 
more accurately, — from radar probes. Radar probes resulted in a radius 
of Venus between 6050 and 6056 km. Consequently, the flight of Mariner-5 
gave physical characteristics of Venus' atmosphere from an altitude of 70 km 
to 32 km. The altitude scale was defined as 8.9 km for the lower boundary, 
and the values of the temperature were found to be about 400° K and a pressure 
of about 6 atm. The pressure and temperature pattern, obtained from this 
experiment, agrees excellently with the pattern of these quantities in the 

67 



experiments with the unmanned spacecraft Venera-4 and Venera-5. If it is 
applied up to the very lowest level of the atmosphere, with a radius of 
6053 km, then figures are found that are similar to those given above, that 
is, a temperature of about 770° K and a pressure of about 100 atm. 

In the entire experiment of Mariner-5, precise knowledge of the entire 
geometry of the phenomenon is of primary importance, that is, the mutual 
distribution of the points M^ , M , ..., of Venus and the Earth, and the value 
of the planet's radius. Change in frequencies of the signals is accomplished 
with great accuracy up to 0.08 Hz, which made it possible to follow with high 
accuracy the trajectory of the unmanned spacecraft Mariner-5 for the entire 
trip. In this case celestial-mechanical computations were carried out in 
parallel, especially when the spacecraft was nearing Venus, since Venus /69 
produced a very substantial change in the orbit of the craft relative to the 
Sun (its velocity relative to the planet grew from 3.05 to 8.56 km/sec, and 
the frequency of the received signals changed by 95,000 Hz because of this). 
American scientists consider that, as a result of all the measurements and 
computations, the position of Mariner-5 relative to the center of Venus was 
known for the entire approach time within an error no greater than 0.2 km. 
But in order to obtain such high accuracy, the motion of Venus must be known 
as precisely as possible. The necessary data, reinforced by the results of 
radar observations, were given by celestial mechanics. 

We should note the fact that in the radioscopy of the Martian atmosphere 
it is not the signal itself from Mariner that was observed, but a retransla- 
tion by it of the signal sent from Earth. This signal was regulated by the 
oscillations of rubidium atomic source which ensured its superhigh stability. 
In investigating the atmosphere of Venus, such a technique was not used, 
since the double passage of the signal through its superdense atmosphere 
threatened too large an attenuation of the signal's strength. 

Greenhouse effect . The greenhouse effect of a planet's atmosphere, just 
as in our hothouses covered with glass, is based on the fact that solar 



68 



radiation, heating the planet's surface, passes through the atmosphere 
comparatively freely, and the radiation from the heated surface of the 
planet cannot go beyond the limits of the atmosphere, since it is absorbed 
by the gases which heat them. In our hothouses glass plays this role. It 
does not prevent the short-wave solar radiation from penetrating inside the 
hothouses, but it does restrain the radiation of heat from the hothouse to 
the outside, since this radiation is of the long-wave type, and the glass 
for the long-wave. Infrared radiation is opaque. Not every atmosphere 
possesses such a restraining effect: for example, hydrogen, helium and 
nitrogen atmospheres do not have this property. 

Quite another situation is involved with an atmosphere containing carbon 
dioxide, water vapors, and ozone. If we investigate the spectrum of any 
source, the light of which has travelled a sufficiently long path in carbon 
dioxide or in water vapors, then in the infrared band of the spectrum we will 
detect a number of very dark bands, indicating the absorption of radiation. /70 
These bands give information on the radiation at a wavelength of 1-4 y (mainly 
water vapors) , but at 4 and 15 v carbon dioxide, and at 6 and 50 y — water 
vapors almost completely retard the radiation. A planet radiates basically 
between 10 and 15 y, if its temperature equals 250° K, and between 4 and 15 y 
at a temperature of 600° K. Fortunately, for astronomy, these bands do not 
merge with one another, if we examine the radiation of celestial bodies after 
passing through the Earth's atmosphere. Spectral "windows of transparency" 
are found in them, that is, wavelength intervals of the infrared band in which 
the absorption is not high, and celestial bodies can be observed without 
losses due to absorption. 

However, the Earth's atmosphere is not rich with carbon dioxide and 
water vapors. Venus is a different situation, where more than 90% of the 
atmosphere consists of carbon dioxide, and the absolute content of water 
vapor is significantly higher than in the atmosphere of the Earth. Thus, 
all the absorption bands of these gases are merged together, and the natural 
heat radiation of the planet, if it has a temperature of 200-700° K, cannot 
exceed the limits of even the lowest layers of the atmosphere, — it will 

69 






,3 




cloud 
'^^ layer 



|T=700°K 



■yd \ 



k^Ett 



P^-w^o -ha:?^ Jfifeav ;., 






Figure 20. Greenhouse effect In the atmosphere 
of a planet rich with carbon dioxide and water 
vapors. The solar energy flux arriving at a 
given site on the planet is shown by the 
light (wedge-shaped) band. In the cloud lay- 
er a significant part of this energy is 
scattered, which is shown by the decrease in 
band width. This scattering continues farther 
below the clouds due to the encounter of the 
photons with the gas molecules and the solid 
and liquid particles, suspended in the at- 
mosphere. A very small part of the radiation, 
which is absorbed here and heats the planet, 
reaches the surface of the planet. Simul- 
taneously with scattering in the atmosphere 
an insignificant absorption takes place (the 
gray band inside the light one) thus heating 
the atmosphere. The heated surface of the 
planet emits long-wave radiation which is 
absorbed by the atmosphere as a whole (atten- 
uation of the light points with altitude) , 
with the exception of the radio waves of 3-50 
cm, which leave the atmosphere without hin- 
drance (wavy lines) . Convective currents 
(the weak spiral lines) also leave the hot 
surface of the planet into the atmosphere. 

A luminous energy flux 
from the Sun reaches the highly positioned cloud layer of the planet. This 
is shown by the light shape in the center of the drawing, the width of which 

70 



be absorbed. Of course, it 
will be partially reradiated, 
but a considerable part of 
it will go into heating the 
gases, and the reradiation 
will go to all sides in- 
cluding back to the surface. 
As a result, the thermal 
radiation flux going out- 
side is decreased almost to 
zero. But the heat flux 
leaving the Sun does not 
cease, the surface of the 
planet is heated, and only 
when equilibrium is estab- 
lished between the freely 
arriving heat and the natural 
heat, which leaves the planet 
"with difficulty", is there 
a temperature equilibrium 
established at a certain 
comparatively high level. 

Figure 20 shows this 
with a schematic represen- 
tation of the conditions of 
heat transport in the at- 
mosphere of a planet, as 
applied specifically to 
Venus . 



J 



I 



' corresponds to the strength of the flux. After encountering the cloud cover, 
the solar light is scattered by the clouds. The scattering is very great. 
It continues also below the clouds where the flux undergoes strong attenuation, /71 
; and is propagated farther down, the greater it is scattered, creating a 
I luminous field similar to that which exists on Earth on a cloudy day (this is 
' shown on the drawing by an overall semi-light background) . Let us recall that 
I the scattering involves the scattering of atoms, molecules, and particles 
; reradiating the incoming photons, without changing their frequencies. The /72 
situation is that the almost unchanged solar light, scattered by the clouds or 
penetrated from under the cloud layer, is emitted back into space by Venus, — 
about 75% of all the light incident on it. If we speak about all the solar 
energy, including the infrared and the ultraviolet bands of the spectrum, then 
for the planet there remains only 28%; and 72% is reflected and lost irrevocably. 
There 28% are absorbed, that is, they either go into restructuring the internal 
structure of the atoms or molecules, and then into heating the gas, or — 
unlike scattering — the absorbed photons are reradiated at another wavelength, 
but such reradiated photons are recaptured and also go into heating the gas. 
This process of progressive absorption is shown on Figure 20 by the tapering 
gray wedge shown inside the outer light wedge of the scattered energy flux 
reaching the surface of the planet in a negligible amount. 

At the same time, the hot surface of the planet radiates a rather large 
amount of energy (the light points on Figure 20) . The upward energy flux is 
very rapidly attenuated because of absorption in the carbon dioxide and water 
vapors. Nothing reaches the cloud layer; even convection (on Figure 20 the 
spiral columns) is in no position to help transport the heat. Therefore, 
measurements of the natural heat flux from Venus in the infrared band (after 
subtracting the solar energy flux reflected from the clouds) leads to a 
temperature of 240° K, which we attribute to the cloud layer. Only radiation 
through radio waves in the band from 3 cm to 50 cm reaches us unimpeded from 
the surface. Neither the dense atmosphere nor the clouds affect it, and, 
therefore, with their help the real temperature on the surface of Venus is 
about 700° K. 



71 



TABLES OF PHYSICAL CHARACTERISTICS OF THE 
MAJOR PLANETS AND THE MOON 



Mean distance from the Sun 

Eccentricity of orbit 

Inclination of orbital plane to ecliptic 

Rotation period around the Sun 

Synodic rotation period 

Mean rate of motion in orbit 

Diameter from radar measurements 

Diameter from optical measurements 

Angular diameter, seen from the Earth: 

(a) when Mercury moves along the 
Sun's disk ) in November 



MERCURY 








a 


0.387 A.u/*' 




e 


0.206 


liptic 


1 


7°0'15" 




P 


88.0 days 




S 


115.9 days 




V 


47.9 km/ sec 




°0 


4860 + 4 km 




D 


4850 + 40 km 



in May 

(b) in mean (by distance) elongation 

Area of disk in average elongation 

Area of disk, visible from Sun at mean 
distance from it 

Mass in solar masses 

Mass in Earth masses 

Absolute mass 

Volume in Earth volumes 

Mean density 

Rotation period around axis (stellar days) 

Inclination of equator to orbital plane 

Moment of inertia 

Acceleration of force of gravity at 
equator 



d" 


9.8" 


d 


12,1" 


d 


7.3" 


to 


-9 
I'lO sterad 


Q 


1.3 '10 sterad 


m 


1:6021000 


gji 


0.956 


aji 


3.303-10^^ g 


p 


0.0553 
5.59 g/cm^ 


p' 


58.65 days 


1' 


7° 


unknown 


8„ 


372 cm/sec 



111 



(*) 



A.U. = astronomical unit, equal to the mean 
Sun; 1 A.U. = 149,600,000 kilometers. 



distance of the Earth from the 



72 



Acceleration of force of gravity in units of 
Earth acceleration 

Critical (parabolic) velocity at which a 
body leaves the planet 

Stellar magnitude during the time of the 
mean(by distance) superior conjunction in 
the V system. 

Stellar magnitude in elongation (as a func- 
tion of distance from the Sun) in the 
V system. 

Index of yellowness (excess over the color 
index of the Sun) 

in the system B-V 

in the system B-I 

Visual spherical albedo 

Thermal spherical albedo 

Equilibrium mean temperature at a mean 
distance from the Sun 

Equilibrium mean temperature for the 
subsolar point (computed) 

From measurements in infrared rays 

Dark side has a temperature no higher than 

In the microwave region, the following 
mean brightness temperatures over the 
disk (at a mean distance from the Sun) 
are measured at : 

X = 0.34 cm 

0.86 cm 

1.53 cm 

3.5 cm 

10 . 6 cm 

11.3 cm 

Dependence of T, on phase 

Atmosphere 

The amount of CO. determined at the limit 



V 



0.38 

4.3 km/sec 



-i^'.yi 



from 



-0'".3 to +0'^.6 



\ 



comp 



+0"'.30 
+0°^.93 
0.056 
0.09 

505° K 



618° 


K 


613° 


K 


250° 


K 



200 - 220° K 

404 ± 40° 

465 + 115° 

390 + 100° 

290 + 40° 

290 + 40° 
unconfirmed 
unconfirmed 
from 1.5 to 3.5 m-atm 



i74 



N and Ar and, in the upper layers — CO and as a result of dissociation 
2 ^ 

of carbon dioxide are also theoretically possible. Mercury has no satellites. 



73 



VENUS 
Mean distance from Sun 

Eccentricity of orbit 

Inclination of orbital plane to plane of 
ecliptic 

Rotation period around Sun 

Synodic rotation period 

Mean rate of motion in orbit 

Diameter over surface 

Diameter over level of cloud layer 

Diameter over level of obscuration of 
Regulus 

Angular diameter seen from the Earth 

in inferior conjunction 

in superior conjunction 
Area of disk seen from the Earth: 

in inferior conjunction 

in superior conjunction 

Area of disk seen from the Sun at a mean 
distance from it 

Mass in solar masses 

Mass in Earth masses 

Absolute mass 

Volume in earth masses 

Mean density 

Rotation period around axis (stellar 
days); retrograde rotation 

Rotation period of visible surface (cloud 
layer) ;retrograde rotation 

Inclination of equator to orbital plane 

Moment of inertia 

Acceleration of force of gravity at 
equator 



a 


0.723 A.U. 


e 


0.007 


1 


3°23'40" 


P 


224.7 days 


S 


583.9 days 


V 


35.0 km/ sec 


°o 


12105 ±4 km 


D 


12200 ±20 km 



D' 12338 ±10 km 



d 60.8" (max. 65.2") 
d 9.8" (min. 9.5") 

—8 
03 6.8-10 sterads 

-9 
(0 1.8 "10 sterads 



—8 
1.0* 10 sterads 



1.408250 
0.815 



27 



gjl 4.867-10 
Vq 0.861 g 
P 5.22 g/c 



P' 243.0 -0.5 days 

P" 4 days 
t' 178° (*) 
unknown 

2 
g 886 cm/sec 



III 



(*) 

This angle is equal to 2 , but the directions of the axial and orbital 

motions are opposite to one another. 



74 



Acceleration of force of gravity In units 
of earth acceleration 

Critical (parabolic) velocity at which a 
body leaves the planet 

Stellar magnitude during time of mean (by 
distance) superior conjunction in the 
system V 

Stellar magnitude during time of inferior 
conjunction when the planet is located 
precisely between the Sun and the Earth. 

The same near inferior conjunction 

Maximum brightness (before or after inferior 
conjunction of 35 days) 

Index of yellowness (excess over color index 
of Sun) in the system 

Visual spherical albedo 

Thermal spherical albedo 

Equilibrium mean temperature (computed) 

Actually abservable temperature of cloud 
layer over the disk (from Infrared 
measurements) without confirmed differ- 
ence in night and day side 

Measured in the microwave region at: 

X <_ 0.3 cm 

X >_ 2 cm 

X >^ 21 cm 

By direct measurement from unmanned 
spacecraft Venera-4, Venera-6, and 
Marlner-5 of the surface temperature 

No confirmed indications that the night side 
of Venus is colder than the day side 

Chemical composition of the atmosphere from 
unmanned spacecraft Venera-4 and Venera-6: 

carbon dioxide C0„ 



Be' 


0.90 


V 

e 


10.3 km/sec 




-S^'.Sl 




-0"^.l 




-s'^.s 




-4". 45 


B-V 


-0^19 


A 

V 


0.76 


h 


0.77 + 0.07 




229° K 



comp 



nitrogen N~ 

water H„0 

other gases: CO, O™, HCl, HF 



225 - 235 - 240° K 

^ 300° K 
^ 700° K 
<. 600° K 

'^> 750° + 100° K 



97 + 4% 

no more than 2% 

0.05% 

admixtures 



75 



Atmospheric pressure on surface 
Altitude of uniform atmosphere: 

at its base 

at level of obscuration of Regulus 

Optical thickness of cloud layer in visible 
band 

Cloud layer has large heterogeneities 
(partial gaps) 

Maximal electron concentration in the 

ionosphere at an altitude of about 90 km 
over the cloud layer, by day (by night 
it is 50 times smaller) 



100 + 40 atm 



H 13 km 
H 6.8 km 



Tq 70 + 40 



m. 



n 5.5-10^ cm ^ 
e 



No magnetic field was detected on Venus (as the dipole is 3000 times 
weaker than on Earth) 



EARTH 



Mean distance from Sun 

Eccentricity of orbit 

Rotation period around Sun 

Mean rate of motion in orbit 

Equatorial diameter 

Polar diameter 

Mean diameter 

Flattening e = (D^ - D^) rD^ 

Area of disk visible from the Sun at an 
average distance from it 

Mass in solar masses 

Absolute mass 

Volume 

Mean density 

Rotation period around axis (stellar days) 

Inclination of equator to orbital plane 
(ecliptic) 



a 


1.000 A.U. 


e 


0.017 


P 


365.256 days 


V 


29.8 km/ sec 


°E 


12,756.3 km 


°P 


12,713.6 km 


D 


12742.1 km 


e 


1 : 298.2 


fi 


0.57-10"^ sterad 


SW 


1 : 332944 


m. 


5.976-lO^^g 


!o 

p 


1.083-10^^ cm-^ 
5.517 g/cm-^ 


p 


23 hr. 56 mln. 4.099 sec 



23° 27' 



76 



Moment of Inertia (in units ofTOR ) I 

Ratio of centrifugal force to force of gravity 
at equator $ 

Acceleration of force of gravity at equator 



Critical (parabolic) velocity at which a body 
leaves the planet 

Stellar magnitude seen from the Sun in the 
system V 

Index of yellowness (excess over color index 
of Sun) in the system 

Visual spherical albedo 

Mean temperature over surface of Earth 

Maximal temperature for the subsolar point 

The Earth radiates into space as an absolute 
black body with a temperature of 

Atmosphere of the Earth 

nitrogen 

oxygen 

argon 

water 

carbon dioxide 

neon 

methane 

other gases in the form of impurities 
as a whole less than 

Atmospheric pressure at sea level 

Altitude of uniform atmosphere 
Magnetic field: dipole moment 

horizontal component 

vertical component 
((|) - geomagnetic latitude) 



S. 



V 



B-V 



rad 



^2 

°2 
Ar 

CO 2 

Ne 

CH, 



H 
Z 



0.334 



0.0035 



978.044 cm/sec 



11.2 


km/ sec 


-3"^. 


87 


-0^. 


6 


0.39 




285° 


K 


349° 


K 



250° K 

62,500 cm-atm 

16,800 cm-atm 

7440 cm-atm 

from 3000 to 5000 cm-atm 

220 cm-atm 

14 cm-atm 

1.2 cm-atm 

2 cm-atm 

1 atm = 1013.25 mbar = 
1033.23 G/cm^ 



8 km 



.25 



8.06*10 elem . units. 
0.315 cos ()> gauss 
0.630 sin (j) gauss 



77 



MRS 

Mean distance from Sun 

Eccentricity of orbit 

Inclination of orbital plane to ecliptic 
plane 

Rotation period around Sun 

Synodic rotation period 

Mean rate of motion in orbit 

Equatorial diameter 

Polar diameter 

Flattening e = (D^ - Dp) :Dp 

Djniamically determined flattening 

Angular diameters, seen from Earth during 
time of mean (by distance) opposition: 

equatorial 

polar 

Area of disk in mean opposition 

Area of disk visible from Sun at mean 
distance from it 

Mass in solar masses 

Mass in Earth masses 

Absolute mass 

Volume in Earth volumes 

Mean density 

Rotation period around axis (stellar days) 

Inclination of equator to orbital plane 

2 
Moment of inertia (in units of5DlR ) 

Ratio of centrifugal force to force of 
gravity at equator 



a 


1.524 A.U. 


e 


0.093 


i 


1°51'0" 


P 


1.881 years 


S 


779.9 days 


V 


24.1 km/sec 


°E 


6,800km (*) 


°P 


6746 km (*) 


e 


1 : 125 (*) 




1 : 190 



17.9" 

17.76" 

—8 
0.6-10 sterad 



n 


0.7 '10 sterad 


Ti 


1 : 3111000 


m 


0.1078 


m 


6.443-10^^ g 


!o 

p 


0.150 
3.97 g/cm^ 


p' 


24 hr. 37 min. 22.668 sec 


. T 

1 


23°59' 


I 


0.389 



0.0043 



^ ^The values of D and D shown here are derived from optical measurements 
with a maximal error of + 20 km. From them the value of the mean diameter 

(2 D„ + D„) ; 3 = 6769 km is found to be in good agreement with the mean value 

E P 
of 6758 km derived from radio eclipse by Mariner-4. But the value of flat- 
tening computed from them is high, and contradicts the value determined 
dynamically from the motion of the satellites. 



78 



Acceleration of force of gravity at equator 

The same In units of Earth acceleration 

Critical (parabolic) velocity at which a 
body leaves the planet 

Stellar magnitude during time of mean 
opposition in the system 

In superior conjunction with the Sun, 
the planet is weaker by 

Index of yellowness (excess over color 
index of Sun) 

in system B-V 

in system U-I 

Visual spherical albedo 

Thermal spherical albedo 

Equilibrium temperature at mean distance 
from Sun 

The same for the subsolar point (computed) 

From measurements in the infrared band, the 
mean brightness temperature over the disk 
and the temperature of the subsolar point: 

at mean distance from Sun 

in perihelion 

in aphelion 

Mean brightness temperature over disk 
from measurements in microwave region 
at: 

X = 0.34 cm 

3.15 cm 

6 cm 

10 cm 

21 cm 

Chemical composition of atmosphere: 

carbon dioxide 

carbon monoxide 

water: by precipitation from 
atmosphere a layer Is formed with 
a thickness of 



8e 


372 cm/ sec 


8e 


0.380 


V 

e 


5.03 km/ sec 


V 


-2"'.01 , 


AV 


3^.41 





+0"^. 


71 




+1"^. 


93 


A 

V 


0.16 




h 


0.26 


+ 0.05 


comp 
^0 


216° 
306° 


K 
K 


^b 


225° 


K 




286° 


K 




300° 


K 




273° 


K 



190° + 40° K 
218° + 50° K 
192° + 28° K 
177° + 17° K 
190° + 40° K 



CO2 75+15 m-atm 



CO 



traces 



H2O 35 y 



79 



In the upper atmosphere, as a result of 

dissociation, atoms of H, 0, C 

Other possible, but unobserved components N„ , Ar 

Atmospheric pressure on surface p 20 > p > 6 mbar /yg 

Altitude of uniform atmosphere H 13 km 

Ionosphere only on day side with maximal c 3 

concentration of electrons n 1.6 • 10 cm 

e 

Magnetic field None observed 

Mars has two satellites, Phobos and Deimos, with a diameter of 15 - 10 km, 
moving in the equatorial plane of the planet very near it (at distances of 
9.37 and 23.52 thousand kilometers), with a period, respectively, of 0.319 and 
1.262 days. In mean opposition they appear as objects of 11™ - 12™. 



Mean distance from Sun 

Eccentricity of orbit 

Inclination of orbital plane to plane of 
ecliptic 

Rotation period around Sun 

Synodic rotation period 

Mean rate of motion in orbit 

Equatorial diameter 

Polar diameter 

Flattening e = (D^ - D^) rD^ 

Dynamically determined flattening 

Angular diameter, seen from Earth in 
mean opposition: 

equatorial d„ 46.5" 

E 

polar dp 43.7" 

Area of disk seen from Earth in mean 

opposition u 1.6'10~ sterad 

The same from the Sun at mean distance 

from it a 1.04'10~ sterad 



80 



JUPITER 








a 


5.203 A.U. 




e 


0.048 


ane of 


1 


1°18'17" 




P 


11.862 years 




S 


398.9 days 




V 


13.1 km/sec 




h 


141,700 km 




°P 


133,100 km 




e 


1 : 16.5 
1 : 15.34 



Mass in solar masses 

Mass in Earth masses 

Absolute mass 

Volume in Earth volumes 

Mean density 

Rotation period of visible surface (cloud 
layer) : 

in the latitudinal limits +12° 

for the middle latitudes 

Rotation period of decimeter radiation 
carriers 

The magnetic axis rotates with the same 
period relative to the axis of visible 
rotation; angle between them 

Inclination of equator to orbital plane 

2 
Moment of inertia (in units ofOTR ) 

Ratio of centrifugal force to force 
of gravity at equator 

Acceleration of force of gravity at 
equator 

The same in units of Earth acceleration 

Critical (parabolic) velocity at which a 
body leaves the planet 

Stellar magnitude during time of mean 
opposition in the system V 

In superior conjunction with the Sun, the 
planet is weaker by 

Index of yellowness (excess over color index 
of Sun) 

in system B-V 

in system U-I 

o 

Visual spherical albedo (X = 5500 A) 

Thermal spherical albedo 

Equilibrium mean temperature over disk 
(computed) 



an 
fat 

^0 



11 



AV 



h 



comp 



1 : 1047.39 

317.82 

30 
1.899-10''" g 

1347.0 

1.30 g/cm^ 



9 hr. 50 min. 30.000 sec. 
9 hr. 55 min. 40.632 sec. 



Ill 9 hr 55 min 29.37 sec. 





10° 


i' 


3° 04' 


I 


0.26 



0.084 

2.301 cm/sec 
2.35 

57.5 km/sec 



-2"^. 55 



0"^.85 



0"^.20 
0"^.27 
0.67 
0.45 



110° K 



81 



Actually observed brightness temperature on 
disk from measurements: 

in infrared band 

in 8 - 14 p band 

in 10 - 14 jj band (color) 

From measurements in the microwave region 

at X = 0.2 cm the brightness is 

2 cm 

8.6 cm 

21 cm 

Over the rotational band, methane molecules 
X =11, 070 A; the rotation temperature 

Chemical composition of the atmosphere above 
the cloud layer: 

molecular hydrogen (spectrally) 

helium (theoretically) 

methane (spectrally) 

ammonia (spectrally) 

Altitude of uniform atmosphere 



rot 



«2 
He 

NH„ 



126° + 2° K (1964) 
128° (1963) 
125° 

170° + 80° K 

150° 

149° + (1967) 

400° ? 

200° + 20° K 

180° + 20° K 
85 + 15 km-atm 
26 km-atm 
100 m-atm 
5 m-atm 
8 km 



Jupiter has 12 satellites of which four (the Galilean satellites) are 
large celestial bodies comparable in size to the inner planets and the Moon. 
The others are small with diameters on the order of hundreds of kilometers 
or less. The nearest, Amalthea, revolves around the planet in 2.5 days, 
and the remotest, the ninth, in 758 days. Satellites 8, 9, 11, and 12 have 
a direction of orbital motion, opposite that of Jupiter around its axis and 
around the Sun. 



SATUBN 



Mean distance from Sun 

Eccentricity of orbit 

Inclination of orbital plane to plane 
of ecliptic 



a 
e 



9.539 A.U. 
0.056 

2°29'22" 



181 



82 



E 



Rotation period around Sun 

Synodic rotation period 

Mean rate of motion In orbit 

Equatorial diameter 

Polar diameter 

Flattening e = (D„ - D ) : D 

Dynamically determined flattening 

Angular diameter, seen from Earth in mean 
opposition: 

equatorial 

polar 

Area of planet's disk seen from Earth in 
mean opposition 

The same from the Sun at mean distance 
from it 

Mass in solar masses 

Mass in Earth masses 

Absolute mass 

Volume in Earth volumes 

Mean density 

Rotation period of surface (cloud layer) : 

in latitude range + 25° - 30° 

at other latitudes 

Inclination of equator toward orbital plane 

. 2 
Moment of inertia in units ofSKR 

Ratio of centrifugal force to force of 
gravity at equator 

Acceleration of force of gravity at equator 

The same in units of earth acceleration 

Critical (parabolic) velocity at which a 
body leaves the planet 

Stellar magnitude (with the exception 
of the brightness of the ring) in mean 
opposition in the system 

In superior conjunction with the Sun the 
planet is weaker by 



p 


29.458 years 


s 


378.1 days 


V 


9.6 km/sec 


°E 


120,670 ± 600 km 


°P 


109,110 ± 600 km 


e 


1 : 10.4 




1 : 10.2 



19.5" 
17.6" 



.-8 



0.63*10 sterad 



-8 



n 


0.51-10 " sti 


an 


1 : 3500.5 


an 


95.112 


m 


5.684-10^^ g 


!o 

p 


770.5 
0.71 g/cm^ 



P 10 hr. 14 mln. 

P^ 10 hr. 40 mln. 

1' 26°44' 

I 0.21 

$ 0.142 

2 

g 944 cm/ sec 

g 0.965 

V 37 km/sec 
e 

V +0™.67 
AV +0^.46 



83 



The ring introduces additional brightness 
which, in stellar magnitudes, is expres- 
sed by the terms + 0.44 (j) - 2.60 sin B + 
1.25 sin B, where (f> is the phase angle, 
B is the angular elevation of the Earth 
above the plane of the ring. 

At maximal opening of the ring, that is, 
when B = 28° , the stellar magnitude 
of the planet is smaller by 

Yellow index (excess over AV by the color 
index of the Sun) in the system 

Visual spherical albedo 

Mean equilibrium temperature over disk 

Brightness temperature from measurements 
in the infrared band (different authors) 

From measurements in the microwave region at 

X = 0.86 cm 

1 . 53 cm 

3 . 45 cm 

6 cm 

10 cm 

21 cm 

Chemical composition of atmosphere above 
cloud layer: 

molecular hydrogen 

methane 

no helium observed 

ammonia 

Rings of Saturn 



AV 



B-V 



comp 



«2 
CH, 

He 



0"^.95 



f0'".41 
0.69 
80° K 



from 85° to 125° K 

96° + 20° K 
146° + 23° K 
106° + 21° K 
217° + 30° K 
196° + 44° K 
303° + 50° K 



'V' 40 km-atm 
'^ 350 m-atm 
undoubtedly exists 
unconfirmed 



Ring A, outer, brightness moderate at dis- 
tance from center of planet Cassini scale 

Ring B, middle, brightest, at distance 
from center of planet - Dark space 

Ring C, inner, dark (rigid, inner boundary 
not sharp) , at distance from center 
of planet of 



from 138 to 120 thousand 
km 

from 116 to 90 thousand 

km 

from 89 to 71 thousand km 



84 



Thickness of rings 

Hypothetical mass of rings In Satumi masses 



2.8 + 1.5 km 
10"^ - 10-5 



Saturn has ten satellites of which only one. Titan, possesses planetary 

-4 
dimensions (D = 4950 km) and significant mass (2. 4 "10 of the planet's 

mass). The nearest, Janus, (discovered in 1966) moves around the planet at 

a distance of 157.5 thousand kilometers with a period of 18 hours and its 

diameter is estimated to be 350 km. The remotest, Phoebe, revolves around 

the planet for 550 days in the retrograde direction, at a mean distance of 

13 million kilometers. 



URANUS 



Mean distance from Sun 

Eccentricity of orbit 

Inclination of orbital plane to plane of 
ecliptic 

Rotation period 

Synodic rotation period 

Mean rate of motion in orbit 

Equatorial diameter 

Polar diameter 

Flattening e + (D^ - D^,) : D^ 

Angular diameter seen from Earth in mean 
opposition: 

equatorial 

polar 

Area of disk, seen from Earth in mean 
opposition 

The same from the Sun at mean distance 

Mass in solar masses 

Mass in earth masses 

Absolute mass 



a 19.182 A.U. 
e 0.047 



1 


0°46'23" 


p 


84.015 years 


S 


369.7 days 


V 


6.8 km/sec 


\ 


49,130 ± 100 km 


°P 


48,200 ± 1000 km 


e 


1 : 53 



"^E 


3.73" 


S 


3.66" 


(0 


2. 5 •10"''"° sterad 


Q 


2.3-10""'"° sterad 


SDl 


1 : 22934 


n 


14.517 


ftn 


8.676-10^^ g 



85 



_0 

p 

p' 
i' 
I 



55.9 

1.47 g/cm 
10.8 hours 
98° (*) 

0.236 

2 
967 cm/sec 

0.99 

21.6 km/sec 



+ 5"',52 



- 0' 



.m 



.m 



Volume in Earth volumes 

Mean density 

Rotation period around axis (stellar days) 

Inclination of equator to orbital plane 

2 
Moment of inertia (in units ofOTR ) 

Acceleration of force of gravity at equator 

The same in units of Earth acceleration 

Critical (parabolic) velocity at which a body 
body leaves the planet 

Stellar megnitude during time of mean 
opposition in the system V 

Yellow index (excess over color index of 
Sun) 

In system B-V 

in system U-I 

Visual spherical albedo 

Mean equilibrium temperature over disk 

Temperature measured in the infrared 
region in the range of 17.5 - 25 y 

Brightness temperature measured in micro- 
wave region at 

X = 1.9 cm 

3.75 cm 

6 cm 

11.3 cm 

Rotational temperature in CH, absorption band 

The same in the H absorption band 
Chemical composition of atmosphere: 

large amount of hydrogen 
theoretically large amount of helium 

7*) 

The^direction of the axial rotation is retrograde; therefore, we assume 



comp 



07 
- 1"', 62 
0.93 (**) 
60° K 

55° + 3° K 



^b 


220° + 35° K 




130° + 40° K 




100° + 35° K 




128° + 40° K 


\ot 


63° + 10° K 


T 
rot 


124 ± 30° K 


^-2 





(**) 



The largest of the planets in the solar system. 



86 



abundance of methane 



Pressure at the boundary of the cloud layer 



CH, from 3 to 150 km-atm, based 
on various estimates of the 
thickness of the CH^ ab- 
sorption band in the 
planet's spectrum. 

p 3 atm 



Uranus has five satellites. All of them are small (from 100 to 500 km 
in diameter). They move practically in circular orbits, lying almost in the 
planet's equatorial plane with periods from 1.4 to 13.5 days; the direction 
of motion of the satellites coincides with the direction of Uranus ' rotation 
— that is, it is retrograde. 



NEPTUNE 



Mean distance from Sun 

Eccentricity of orbit 

Inclination of orbital plane to plane of 
ecliptic 

Rotation period around Sun 

Synodic rotation period 

Mean rate of motion in orbit 

Diameter from optical measurements 

Diameter at level of half of loss of bright- 
ness of the star during obscuration by 
Neptune 

Flattening 

Dynamically determined compression 

Angular diameter, seen from Earth in 
mean opposition 

Area of planet's disk seen from Earth in 
mean opposition 

The same from the Sun at mean distance 

Mass in solar masses 

Mass in Earth masses 



a 


30.057 A.U. 


e 


0.009 


i 


1°46'22" 


P 


164.788 years 


S 


367.5 days 


V 


5.4 km/sec. 


D 


47,000 +2000 km 



D' 50,450 ±60 km 

e 1 : 48 

e 1 : 58 

d 2.24" 

0) 0.93-10""^'^ sterad 

a 0.86-10~"'-° sterad 

«Dl 1 : 19340 

a» 17,216 



87 



Absolute mass 

Volume in Earth masses 

Mean density 

Rotation period around axis (stellar days) P' 15.8 hours /85 

Inclination of equator to orbital plane 

2 
Moment of inertia (in units of 9JtR ) 

Ratio of centrifugal force at equator to 
force of gravity 

Acceleration of force of gravity at equator 

Same in units of Earth acceleration 

Critical (parabolic) velocity at which a 
body leaves the planet 

Stellar magnitude during time of mean 
opposition in system V 

Yellow index (excess over color index of Sun) 

in system B-V 

in system U-I 

Visual spherical albedo 

Mean equilibrium temperature over disk 

Mean temperature measured over the disk 
at a wavelength of X = 3.12 cm 

From obscuration of star at level D' 

Significant part of atmosphere composed of: 

hydrogen 

methane 

helium theoretically 
Altitude of uniform atmosphere 

Neptune has two satellites. The nearer, Triton, has planetary dimensions 
and moves around the planet in a retrograde direction at a distance of 15.85 
radii with a period of 5.88 days. The other, Nereid, is very small. It 
revolves around the planet in a posigrade direction at a distance of 250 of 
its radii, with a period of 359 days. 



as 


1.029-10^^ g 


^0 

p 


50.65 
1.88 g/cra^ 


p' 


15.8 hours 


i' 


29° 


I 


0.241 


$ 


0.022 


Se 


1194 cm/sec 


Se 


1.258 


V 

e 


25 km/sec 




+7'".84 




-o'^.is 




-2'".02 


A 

V 


0.84 


T 
comp 


51° K 


^b 


115° + 36° K 


T 


110° - 130° K 


«2 




CH^ 


'V 5 km-atm 


He 




H 


50 - 60 km 



88 



■■■■■IIII^II^HH 



Pluto 

Mean distance from Sun 

Eccentricity of orbit 

Inclination of orbital plane to plane of 
ecliptic 

Rotation period around Sun 

Synodic period of rotation 

Mean rate of motion in orbit 

Diameter 

Angular diameter seen from Earth at mean 

opposition 
Area of planet's disk seen from Earth in mean 

opposition (practically the same as from the 

Sun) 

Mass in solar masses 

Mass in Earth masses 

Absolute mass 

Volume in Earth volumes 

Mean density 

Rotation period around axis (stellar days) 

Stellar magnitude during time of mean 
opposition in system V 

Yellow index (excess over color index of Sun) 

in system B-V 

in system U-I 
Visual spherical albedo 
Mean equilibrium temperature over disk 



(*) 
.(*) 



.(*) 



(*) 



D 



V 



0) 
(A*) 

(**) 
(**) 

(it*) 
P' 



(A* ) 



39.750 A.U. 
0.253 

17°8'.5 
250.6 years 
366.8 days 
4.7 km/sec 
6000 km 
0".23 



I-IO""""^ sterad 

1 : 1,812,000 

0.18 

1.08-10^^ g 

0.096 

3 
10.4 g/cm 

6.39 days 
+ 14.90 



+0"^.17 
+0"^.17 



V 



comp 



0.14 
43° K 



786 



(*) 

It varies significantly for short periods of time as a result of strong 

perturbations from other planets. 

Very unreliable figure. From the nonoccuring obscuration of the star, 
located very near the visible path of the planet, the upper limit was deter- 
mined for the diameter D = 5500 km (but also with a large error) and then 
p = 12.4 g/cm3. However, the mass is not kno^^m accurately (from perturbations 
in the motion of Neptune) and may be two times smaller than the figure given. 



89 



Atmosphere 
Satellites 



unknown 
unknown 



THE MOON 



a 


384,400 ton 


e 


0.055 


1 


5°8'43.4" (* 


P 


27.3217 days 


S 


29.5306 days 


V 


1.023 


D 


3476.0 km 


D' 


0.2725 


d 


31'5.6" 




0.00905 rad 



(**) 



6.45*10 ^ sterad 



-9 



Mean distance from Earth 

Eccentricity of orbit 

Inclination of orbit to plane of ecliptic 

Stellar period of rotation 

Synodic period of rotation 

Mean rate of motion in orbit 

Diameter 

Diameter in units of Earth equatorial 
diameter 

Angular diameter at mean distance from Earth 

or 

Area of disk visible from Earth at mean 
distance 

Same visible from Sun at mean distance 
from it 

Mass in solar masses 

Mass In Earth masses 

Absolute mass 

Volume in Earth volumes 

Mean density 

Rotation period around axis (stellar days) 

Inclination of equatorial plane to plane 
of ecliptic 

Mean inclination of equatorial plane to 
orbital plane 

^ Afith respect to the Earth's equator, the inclinati«n of the Ixmar •rblt 
varies between 23°27* ± 5°9', that is, from 18*18' to 28*36'. 

'Because of perturbations from the solar side, it varies within limits of 
of seven hours. 

Because of eccentricity of orbit, it varies within limits of 13 hours. 

90 



Q 


0.42-10 sterad 


fUi 


1 : 27069400 


OT 


1 : 81.3030 


5W 


7.35-10^^ g 


!o 

p 


0.020 
3.35 g/cm^ 


p' 


27.3217 days 


i" 


1°33' 


i' 


6°41' 



131 



Moment of inertia (in units of R'^) 

Acceleration of force of gravity on surface 

Same in units of Earth acceleration 

Critical (parabolic) velocity at which a 
body leaves the Moon 

Integral brightness at mean half-moon in 
system V 

Yellow index (excess over color index of Sun) 

in system B-V 

in system U-I 

Visual spherical albedo 

Temperature of subsolar point ' 

From measurements in the infrared band 

Rapid cooling during lunar eclipse up to 

Two days after onset of night up to 

Temperature at midnight at the equator 

Mean temperature over the entire surface 

Actually measured brightness temperature 
in the microwave region range from 185° 
to 270° with no explicit dependence on 
wavelength 

Amplitude of radio temperature oscilla- 
tions during lunar days (synodic 
rotation period) varies from 

from (at X = 0.13 cm) 

to (at A = 10 - 20 cm) 
and is practically equal to zero at 
A > 30 cm 

Atmosphere on Moon in Earth units no 
greater than 

Magnetic field on lunar surface 

Magnetic moment 

or in Earth units 



I 


0.39 




g 


162.0 cm/sec 


g 


0.166 




V 

e 


2.37 km/sec 




-12"*. 74 






+0"'.29 






+l"'.29 




A 

V 


0.067 




comp 


387° K 
371° K 
175° K 


(1939) 


T' 


122° K 


(1963) 


\ 


115° K 
274° K 





comp 



^•t given/ 



120 - 115° K 
5 - 7° K 



-12 



10 

< 4y 

20 

< 10 erg/gauss 

<io-6 



Translated for National Aeronautics and Space Administration under contract 
No. NASw 2035, by SCITRAN, P.O. Box 5456, Santa Barbara, California, 93108 



91 



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